Peraluminous lithium aluminosilicates  with high liquidus viscosity

ABSTRACT

The embodiments described herein relate to glass articles that include mechanically durable glass compositions having high liquidus viscosity. The glass articles may include glass compositions having from 50 mol. % to 80 mol. % SiO2; from 7 mol. % to 25 mol. % Al2O3; from 2 mol. % to about 14 mol. % Li2O; 0.4 mol. % P2O5; and less than or equal to 0.5 mol. % ZrO2. The quantity (Al2O3 (mol. %)-R2O (mol. %)-RO (mol. %)) is greater than zero, where R2O (mol. %) is the sum of the molar amounts of Li2O, Na2O, K2O, Rb2O, and Cs2O in the glass composition and RO (mol. %) is the sum of the molar amounts of BeO, MgO, CaO, SrO, BaO, and ZnO in the glass composition. A molar ratio of (Li2O (mol. %))/(R2O (mol. %)) may be greater or equal to 0.5. In embodiments, the glass composition may include B2O3. The glass compositions are fusion formable and have high damage resistance.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority under 35 U.S.C. § 119 ofU.S. Provisional Application Ser. No. 62/579,374 filed on Oct. 31, 2017,the content of which is relied upon and incorporated herein by referencein its entirety.

TECHNICAL FIELD

The present specification generally relates to glass compositions and,more specifically, to peraluminous lithium aluminosilicate glasscompositions having high liquidus viscosities and high fractureresistance.

BACKGROUND

Historically glass has been used as cover glass for electronic devicesbecause of optical properties and excellent chemical durability relativeto other materials. In particular, strengthened glasses have beenidentified for use in electronic devices as well as in otherapplications. As strengthened glasses are increasingly being utilized,it has become more important to develop strengthened glass materialshaving improved survivability, especially when subjected to tensilestresses caused by contact with hard/sharp surfaces, such as asphalt orconcrete, experienced in “real world” use and applications. However,certain types of strengthened glasses having high fracture resistancealso exhibit high liquidus temperatures and low liquidus viscosity. Someglass compositions with low liquidus viscosity are not suitable formanufacture by downdraw forming processes such as the fusion downdrawprocess.

SUMMARY

Accordingly, a need exists for glass compositions which exhibit highfracture resistance and mechanical durability and have relatively highliquidus viscosities (for example, greater than 20 kP) to enable theglass compositions to be formed by fusion forming processes.

According to a first embodiment, a glass article comprises acomposition, the composition comprising greater than or equal to 50 mol.% and less than or equal to 80 mol. % SiO₂, greater than or equal to 7mol. % and less than or equal to 25 mol. % Al₂O₃, greater than or equalto 2 mol. % and less than or equal to 14 mol. % Li₂O, greater than orequal to 0.4 mol. % and less than or equal to 10 mol. % P₂O₅, and lessthan or equal to 0.5 mol. % ZrO₂. The composition has (Al₂O₃ (mol.%)-R₂O (mol. %)-RO (mol. %)) that is greater than zero, where R₂O (mol.%) is the sum of the molar amounts of Li₂O, Na₂O, K₂O, Rb₂O, and Cs₂O inthe composition and RO (mol. %) is the sum of the molar amounts of BeO,MgO, CaO, SrO, BaO, and ZnO in the composition.

In a second embodiment according to the first embodiment wherein, amolar ratio of (Li₂O (mol. %))/(R₂O (mol. %)) in the composition isgreater or equal to 0.5. In a third embodiment according to anypreceding embodiment, the composition has (Al₂O₃ (mol. %)-R₂O (mol.%)-RO (mol. %)-P₂O₅ (mol. %)) that is greater than or equal to −2 mol.%. In a fourth embodiment according to any preceding embodiment, thecomposition has (Al₂O₃ (mol. %)-R₂O (mol. %)-RO (mol. %)-P₂O₅ (mol. %))that is less than or equal to 2 mol. %. In a fifth embodiment accordingto any preceding embodiment, the composition has (Al₂O₃ (mol. %)-R₂O(mol. %)-RO (mol. %)-P₂O₅ (mol. %)) is greater than or equal to −2 mol.% and less than or equal to 2 mol. %.

In a sixth embodiment according to any preceding embodiment, thecomposition has a liquidus temperature of less than or equal to 1300° C.In a seventh embodiment according to any preceding embodiment, thecomposition may also have a liquidus viscosity of greater than 20 kP. Inan eighth embodiment according to any preceding embodiment, thecomposition may have a liquidus viscosity of greater than 50 kP.

In a ninth embodiment according to any preceding embodiment, thecomposition may comprise less than or equal to 14 mol. % R₂O. In a tenthembodiment according to any preceding embodiment, the composition mayfurther comprise greater than or equal to 7 mol. % and less than orequal to 14 mol. % R₂O. In an eleventh embodiment according to anypreceding embodiment, the composition may further comprise less than orequal to 2.5 mol. % K₂O. In a twelfth embodiment according to anypreceding embodiment, the composition may further comprise greater thanor equal to 3 mol. % and less than or equal to 15 mol. % B₂O₃. In athirteenth embodiment according to any preceding embodiment, thecomposition may have (Li₂O (mol. %)+Al₂O₃ (mol. %)) is greater than orequal to two times B₂O₃ (mol. %).

In a fourteenth embodiment according to any preceding embodiment, thecomposition may further comprise greater than or equal to 0.1 mol. % andless than or equal to 6 mol. % Na₂O. In a fifteenth embodiment accordingto any preceding embodiment, the composition may further comprisegreater than 0 mol. % and less than or equal to 5 mol. % MgO. In asixteenth embodiment according to any preceding embodiment, thecomposition may further comprise greater than 0 mol. % and less than orequal to 5 mol. % ZnO. In a seventeenth embodiment according to anypreceding embodiment, the composition may further comprise greater than0 mol. % and less than or equal to 4 mol. % CaO. In an eighteenthembodiment according to any preceding embodiment, the composition mayfurther comprise greater than 0 mol. % and less than or equal to 4 mol.% SrO. In a nineteenth embodiment according to any preceding embodiment,the composition may further comprise less than or equal to 0.35 mol. %SnO₂. In a twentieth embodiment according to any preceding embodiment,the composition may be substantially free of BaO.

In a twenty first embodiment, a glass article comprises a composition,the composition comprising greater than or equal to 50 mol. % and lessthan or equal to 80 mol. % SiO₂, greater than or equal to 7 mol. % andless than or equal to 25 mol. % Al₂O₃, greater than or equal to 2 mol. %and less than or equal to 14 mol. % Li₂O, greater than or equal to 3mol. % and less than or equal to 15 mol. % B₂O₃, greater than or equalto 0.1 mol. % Na₂O, and greater than or equal to 0 mol. % and less thanor equal to 4 mol. % TiO₂. The composition has (Al₂O₃ (mol. %)-R₂O (mol.%)-RO(mol. %)) that is greater than or equal to zero, where R₂O (mol. %)is the sum of the molar amounts of Li₂O, Na₂O, K₂O, Rb₂O, and Cs₂O inthe composition and RO (mol. %) is the sum of the molar amounts of BeO,MgO, CaO, SrO, BaO, and ZnO in the composition. The composition also has(Al₂O₃ (mol. %)-R₂O (mol. %)-RO(mol. %)-P₂O₅ (mol. %)) that is less thanor equal to 2, R₂O (mol. %) is less than or equal to 14 mol. %.

In a twenty second embodiment according to the twenty first embodiment,the composition may have a molar ratio of (Li₂O (mol. %))/(R₂O (mol. %))is greater than or equal to 0.5. In a twenty third embodiment accordingto the twenty first or twenty second embodiment, the composition mayfurther comprise greater than or equal to 0.4 mol. % and less than orequal to 10 mol. % P₂O₅. In a twenty fourth embodiment according to anyone of the twenty first through twenty third embodiments, thecomposition may have (Al₂O₃ (mol. %)-R₂O (mol. %)-RO (mol. %)-P₂O₅ (mol.%)) that is greater than or equal to −2.

In a twenty fifth embodiment according to any one of the twenty firstthrough twenty fourth embodiments, wherein (Li₂O (mol. %)+Al₂O₃ (mol.%)) is greater than or equal to two times B₂O₃ (mol. %). In a twentysixth embodiment according to any one of the twenty first through twentysixth embodiments, wherein the composition further comprises greaterthan or equal to 1.5 mol. % and less than or equal to 6 mol. % Na₂O. Ina twenty seventh embodiment according to any one of the twenty firstthrough twenty sixth embodiments, wherein the composition furthercomprises less than or equal to 0.35 mol. % SnO₂. In a twenty eighthembodiment according to any one of the twenty first through twentyseventh embodiments, wherein the composition has a liquidus temperatureof less than or equal to 1300° C. In a twenty ninth embodiment accordingto any one of the twenty first through twenty eighth embodiments,wherein the composition has a liquidus viscosity of greater than 20 kP.

In a thirtieth embodiment, a glass article includes a composition, thecomposition comprising greater than or equal to 50 mol. % and less thanor equal to 80 mol. % SiO₂, greater than or equal to 7 mol. % and lessthan or equal to 25 mol. % Al₂O₃, greater than or equal to 2 mol. % andless than or equal to 14 mol. % Li₂O, greater than or equal to 0.1 mol.% and less than or equal to 20 mol. % B₂O₃, greater than or equal to 0.1mol. % and less than or equal to 20 mol. % P₂O₅, and less than or equalto 1 mol. % ZrO₂. The composition has (Al₂O₃ (mol. %)-R₂O (mol. %)-RO(mol. %)) that is greater than zero, where R₂O (mol. %) is the sum ofthe molar amounts of Li₂O, Na₂O, K₂O, Rb₂O, and Cs₂O in the compositionand RO (mol. %) is the sum of the molar amounts of BeO, MgO, CaO, SrO,BaO, and ZnO in the composition.

In a thirty first embodiment according to the thirtieth embodimentwherein a molar ratio of (Li₂O (mol. %))/(R₂O (mol. %)) is greater thanor equal to 0.5. In a thirty second embodiment according to thethirtieth or thirty first embodiment, wherein (Al₂O₃ (mol. %)-R₂O (mol.%)-RO (mol. %)-P₂O₅ (mol. %)) is greater than or equal to −2 mol. %. Ina thirty third embodiment according to any one of the thirtieth throughthirty second embodiments, wherein (Al₂O₃ (mol. %)-R₂O (mol. %)-RO (mol.%)-P₂O₅ (mol. %)) is greater than or equal to −2 mol. % and less than orequal to 2 mol. %. In a thirty fourth embodiment according to any one ofthe thirtieth through thirty third embodiments, wherein (Al₂O₃ (mol.%)-R₂O (mol. %)-RO (mol. %)-P₂O₅ (mol. %)) is greater than or equal to−2 mol. % and less than or equal to 2 mol. %. In a thirty fifthembodiment according to any one of the thirtieth through thirty fourthembodiments, wherein the composition comprises less than or equal to 14mol. % R₂O. In a thirty sixth embodiment according to any one of thethirtieth through thirty fifth embodiments, wherein the compositioncomprises greater than or equal to 7 mol. % and less than or equal to 14mol. % R₂O. In a thirty seventh embodiment according to any one of thethirtieth through thirty sixth embodiments, wherein (Li₂O (mol. %)+Al₂O₃(mol. %)) is greater than or equal to two times B₂O₃ (mol. %). In athirty eighth embodiment according to any one of the thirtieth throughthirty seventh embodiments, wherein the composition further comprisesgreater than or equal to 1 mol. % and less than or equal to 6 mol. %Na₂O. In a thirty ninth embodiment according to any one of the thirtieththrough thirty eighth embodiments, wherein the composition furthercomprises greater than 0 mol. % and less than or equal to 0.35 mol. %SaO₂. In a fortieth embodiment according to any one of the thirtieththrough thirty ninth embodiments, wherein the composition has a liquidustemperature of less than or equal to 1300° C. In a forty firstembodiment according to any one of the thirtieth through fortiethembodiments, wherein the composition has a liquidus viscosity of greaterthan 20 kP.

In a forty-second embodiment, a glass article comprises a composition,the composition comprising: greater than or equal to 50 mol. % and lessthan or equal to 80 mol. % SiO₂; greater than or equal to 2 mol. % andless than or equal to 25 mol. % Al₂O₃; greater than or equal to 2 mol. %and less than or equal to 15 mol. % Li₂O; wherein SiO₂ (mol%)≥[4*Li₂O+6*(Na₂O+K₂O)+2.5*MgO+2*(CaO+SrO+BaO)] (mol %), wherein (Al₂O₃(mol. %)-R₂O (mol. %)-RO (mol. %)) is greater than zero, where R₂O (mol.%) is the sum of the molar amounts of Li₂O, Na₂O, K₂O, Rb₂O, and Cs₂O inthe composition and RO (mol. %) is the sum of the molar amounts of BeO,MgO, CaO, SrO, BaO, and ZnO in the composition, wherein a molar ratio of(Li₂O (mol. %))/(R₂O (mol. %)) is greater or equal to 0.35, wherein P₂O₅(mol %)/[(Al₂O₃—R₂O—RO)] (mol %) is greater than or equal to 0.25,wherein TiO₂ (mol %)+ZrO₂ (mol %) is greater than or equal to 0 mol. %and less than or equal to 1 mol. %, wherein a total content of rareearth metal oxides is greater than or equal to 0 mol. % and less than orequal to 0.5 mol %, and wherein A is greater than or equal to 17, where:

A=13.2+P*[(1/673−1(A.P.+273))],

P=0.6/[(1/(A.P.+273))−(1/(T ₁₂+273))],

A.P. is the annealing point in ° C., and

T₁₂ is the temperature in ° C. corresponding to when the glass has aviscosity of 10¹² Poises.

In a forty-third embodiment according to the forty-second embodiment,wherein P₂O₅ (mol %)/[(Al₂O₃—R₂O—RO)](mol %) is greater than or equal to0.8 and less than or equal to 1.25. In a forty-fourth embodimentaccording to the forty-second embodiment wherein P₂O₅ (mol%)/[(Al₂O₃—R₂O—RO)](mol %) is greater than or equal to 0.9 and less thanor equal to 1.1. In a forty-fifth embodiment according to any one of theforty-second through forty-fourth embodiments, wherein a Young's modulusis greater than or equal to 70 GPa. In a forty-sixth embodimentaccording to any one of the forty-second through forty-fourthembodiments, wherein a Young's modulus is greater than or equal to 80GPa. In a forty-seventh embodiment according to any one of theforty-second through forty-sixth embodiments, wherein a fracturetoughness is greater than or equal to 0.7 MPa*m^(1/2). In a forty-eighthembodiment according to any one of the forty-second through forty-sixthembodiments, wherein a fracture toughness is greater than or equal to0.8 MPa*m^(1/2). In a forty-ninth embodiment according to any one of theforty-second through forty-eighth embodiments, wherein A is greater thanor equal to 19.

In a fiftieth embodiment, a consumer electronic product includes ahousing having a front surface, a back surface and side surfaces andelectrical components provided at least partially within the housing,the electrical components including at least a controller, a memory, anda display, the display being provided at or adjacent the front surfaceof the housing. The consumer electronic product further includes a coversubstrate disposed over the display. At least one of a portion of thehousing or the cover substrate comprises the glass article of any one ofthe embodiments disclosed herein.

Additional features and advantages will be set forth in the detaileddescription which follows, and in part will be readily apparent to thoseskilled in the art from that description or recognized by practicing theembodiments described herein, including the detailed description whichfollows, the claims, as well as the appended drawings.

It is to be understood that both the foregoing general description andthe following detailed description describe various embodiments and areintended to provide an overview or framework for understanding thenature and character of the claimed subject matter. The accompanyingdrawings are included to provide a further understanding of the variousembodiments, and are incorporated into and constitute a part of thisspecification. The drawings illustrate the various embodiments describedherein, and together with the description serve to explain theprinciples and operations of the claimed subject matter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 graphically depicts the stress (x-axis) profile across thethickness (y-axis) of the inventive glass compositions after ionexchange strengthening;

FIG. 2A is a plan view of an exemplary electronic device incorporatingany of the glass articles disclosed herein; and

FIG. 2B is a perspective view of the exemplary electronic device of FIG.2A.

DETAILED DESCRIPTION

Reference will now be made in detail to various embodiments of glasscompositions which exhibit improved drop performance and greaterliquidus viscosity, which provides a more mechanically durable glassthat can be produced by fusion downdraw forming processes. Such glasscompositions are suitable for use in various applications including,without limitation, as cover glass for electronics. The glasscompositions may also be chemically strengthened thereby impartingincreased mechanical durability to the glass. The glass compositionsdescribed herein may generally be described as peraluminous lithiumaluminosilicates. Thus the glass compositions described herein comprisesilica (SiO₂), alumina (Al₂O₃), and lithium oxide (Li₂O). In someembodiments, the glass compositions may also comprise alkali oxides inaddition to lithium oxide (such as Na₂O, and/or K₂O for example), andalkaline earth oxides (such as MgO and/or CaO for example) in amountswhich impart chemical and mechanical durability to the glass compositionand liquidus viscosity sufficient to allow the glass composition to beproduced using fusion downdraw forming processes. Moreover, the alkalioxides present in the glass compositions facilitate chemicallystrengthening the glass compositions by ion exchange. In someembodiments, the glass composition may include P₂O₅, B₂O₃, or both,which may be incorporated into the glass composition to improve theliquidus viscosity, damage resistance, or both. Various embodiments ofthe glass compositions will be described herein and further illustratedwith reference to specific examples.

The term “softening point,” as used herein, refers to the temperature atwhich the viscosity of the glass composition is 10^(7.6) poise.

The term “annealing point,” as used herein, refers to the temperaturedetermined according to ASTM C598-93, at which the viscosity of a glassof a given glass composition is approximately 10^(13.2) poise.

The term “T₁₂”, as used herein, refers to the temperature determinedaccording to ASTM C598-93, at which the viscosity of a glass of a givenglass composition is approximately 10¹² poise.

The terms “strain point” and “T_(strain)” as used herein, refers to thetemperature determined according to ASTM C598-93, at which the viscosityof a glass at a given glass composition is approximately 10^(14.7)poise.

The term “liquidus temperature” refers to the temperature above whichthe glass composition is completely liquid with no crystallization ofconstituent components of the glass. The liquidus temperature of theglass is measured in accordance with ASTM C829-81 (2015), titled“Standard Practice for Measurement of Liquidus Temperature of Glass bythe Gradient Furnace Method”.

The term “liquidus viscosity” refers to the viscosity of the glasscomposition at the liquidus temperature of the glass composition. Theliquidus viscosity of the glass at the liquidus temperature is measuredin accordance with ASTM C965-96(2012), titled “Standard Practice forMeasuring Viscosity of Glass Above the Softening Point”.

The term “CTE,” as used herein, refers to the coefficient of linearthermal expansion of the glass composition over a temperature range fromroom temperature (RT) to 300° C. and is determined using a push-roddilatometer in accordance with ASTM E228-11.

In the embodiments of the glass compositions described herein, theconcentrations of constituent components (e.g., SiO₂, Al₂O₃, and thelike) are specified in mole percent (mol. %) on an oxide basis, unlessotherwise specified. Mole percent of a constituent in the glasscomposition refers to the number of moles of the constituent per unitmole of the glass composition times 100.

The term “peraluminous” as used herein refers to glasses where Al₂O₃(mol %) is greater than the sum of the R₂O mol. % (alkali oxides) and ROmol. % (alkaline oxides and ZnO).

The terms “free” and “substantially free,” when used to describe theconcentration and/or absence of a particular constituent component in aglass composition, means that the constituent component is notintentionally added to the glass composition. However, the glasscomposition may contain traces of the constituent component as acontaminant or tramp in amounts of less than 0.05 mol. %.

The term “tramp,” when used to describe a particular constituentcomponent in a glass composition, refers to a constituent component thatis not intentionally added to the glass composition and is present inamounts less than 0.05 mol. %. Tramp components may be unintentionallyadded to the glass composition as an impurity in another constituentcomponent or through migration of the tramp component into thecomposition during processing of the glass composition.

The glass compositions described herein are lithium peraluminousaluminosilicate glass compositions which may generally include acombination of SiO₂, Al₂O₃, and Li₂O, and in some embodiments, mayinclude additional alkali oxides Na₂O, and/or K₂O. The glasscompositions are suitable for chemical strengthening by ion exchange andhave liquidus viscosities sufficiently high so that the glasscompositions may be formed by fusion downdraw forming processes. Afterion exchange, the resultant glasses exhibit greater drop performancecompared to conventional cover glasses for portable electronics. In someembodiments, the glass compositions may also include P₂O₅, B₂O₃, atleast one alkaline earth oxide, or combinations of these. Thesecomponents may be added to further increase the liquidus viscosityand/or improve the mechanical durability and drop performance of theglass. In some embodiments the glass compositions may further compriselesser amounts of one or more additional oxides such as, for example,SnO₂, ZrO₂, ZnO, TiO₂, As₂O₃ or the like, as described herein. Thesecomponents may be added as fining agents and/or to further enhance thechemical durability of the resultant glass.

In the embodiments of the glass compositions described herein, SiO₂ isthe largest constituent of the composition and, as such, is the primaryconstituent of the resulting glass network. SiO₂ enhances the chemicaldurability of the glass and the resistance of the glass composition todecomposition in acid and the resistance of the glass composition todecomposition in water. If the content of SiO₂ is too low, the chemicaldurability and chemical resistance of the glass may be reduced and theglass may be susceptible to corrosion. Accordingly, a high SiO₂concentration is generally desired. However, if the content of SiO₂ istoo high, the formability of the glass may be diminished as higherconcentrations of SiO₂ increase the difficulty of melting the glasswhich, in turn, adversely impacts the formability of the glass. In theembodiments described herein, the glass composition generally comprisesSiO₂ in an amount greater than or equal to 50 mol. % and less than orequal to about 80 mol. %, less than or equal to 75 mol. %, less than orequal to 74 mol. %, less than or equal to 72 mol. %, or even less thanor equal to 70 mol. % and any ranges or subranges therebetween. In someembodiments, the amount of SiO₂ in the glass composition may be greaterthan about 58 mol. %, greater than about 65 mol. %, or even greater thanabout 67 mol. %. In some other embodiments, the amount of SiO₂ in theglass composition may be greater than 70 mol. %, greater than 72 mol. %,or even greater than 74 mol. %. For example, in some embodiments, theglass composition may include from about 58 mol. % to about 80 mol. %,from about 58 mol. % to about 75 mol. %, from about 58 mol. % to about74 mol. %, from about 58 mol. % to about 72 mol. %, or even from about58 mol. % to about 70 mol. % SiO₂. In some other embodiments, the glasscomposition may include from about 65 mol. % to about 80 mol. %, from 65mol. % to about 75 mol. %, from about 65 mol. % to about 74 mol. %, fromabout 65 mol. % to about 72 mol. %, or even from about 65 mol. % toabout 70 mol. % SiO₂. In some other embodiments, the glass compositionmay include from about 67 mol. % to about 80 mol. %, from about 67 mol.% to about 75 mol. %, from about 67 mol. % to about 74 mol. %, fromabout 67 mol. % to about 72 mol. %, or even from about 67 mol. % toabout 70 mol. % SiO₂. In still other embodiments, the glass compositionmay comprise greater than or equal to 58 mol. % and less than or equalto 74 mol. % SiO₂. In some embodiments, the glass composition comprisesgreater than or equal to 65 mol. % and less than or equal to 72 mol. %SiO₂. In still other embodiments, the glass composition may comprisegreater than or equal to 67 mol. % and less than or equal to 70 mol. %SiO₂. In some embodiments, the mol % of SiO₂ in the glass meets thefollowing relationship: SiO₂ (mol%)≥[4*Li₂O+6*(Na₂O+K₂O)+2.5*MgO+2*(CaO+SrO+BaO)] (mol %). Without beingbound by theory, it is believed that the silica content should meet theabove relationship to prevent crystallization of alumina-rich refractoryminerals.

The glass compositions described herein may further include Al₂O₃.Al₂O₃, in conjunction with alkali oxides present in the glasscompositions such as Li₂O, or the like, improves the susceptibility ofthe glass to ion exchange strengthening. More specifically, increasingthe amount of Al₂O₃ in the glass compositions increases the speed of ionexchange in the glass and increases the compressive stress produced inthe compressive layer of the glass as a result of ion exchange. Alkalioxides compensated with Al₂O₃ exhibit greater mobility during ionexchange compared to alkali oxides that are not compensated by Al₂O₃.The Al₂O₃ may also increase the hardness and damage resistance of theglass. However, the liquidus viscosity of the glass decreases withincreasing concentration of the Al₂O₃ in the glass compositions. If theconcentration of Al₂O₃ in the glass compositions is too great, theliquidus viscosity of the glass composition decreases, which may causethe glass composition to crystallize during production in a fusiondowndraw process. In the embodiments described herein, Al₂O₃ is presentin the glass compositions in Al₂O₃ (mol. %), while the alkali oxides arepresent in the glass compositions in R₂O (mol. %), where R₂O (mol. %) isequal to the sum of the mole fractions of Li₂O, Na₂O, K₂O, Rb₂O, andCs₂O.

In some embodiments, the molar ratio (Al₂O₃ (mol. %))/(R₂O (mol. %)) inthe glass compositions is greater than or equal to 1 in order to fullycompensate the alkali oxides with Al₂O₃ and facilitate theaforementioned susceptibility to ion exchange strengthening. Stated inanother way, the glass compositions may have (Al₂O₃ (mol. %)-R₂O (mol.%)) that is greater than or equal to zero, where R₂O is the sum of themolar amounts of Li₂O, Na₂O, K₂O, Rb₂O, and Cs₂O in the glasscomposition. Specifically, the diffusion coefficient or diffusivity D ofthe glass compositions relates to the rate at which alkali ionspenetrate into the glass surface during ion exchange. Glass compositionshaving a ratio (Al₂O₃ (mol. %))/(R₂O (mol. %)) equal to 1 have greaterdiffusivity (i.e., mobility) of the alkali oxide ions through the glasscompositions compared to glasses having the same total alkali content(R₂O (mol. %)) but a ratio (Al₂O₃ (mol. %))/(R₂O (mol. %)) less than 1or greater than 1. Glasses in which the alkali ions have a greaterdiffusivity can obtain a greater depth of layer for a given ion exchangeimmersion time and ion exchange temperature than glasses in which thealkali ions have a lower diffusivity.

In embodiments described herein, alkaline earth oxides (e.g., BeO, MgO,CaO, SrO, and BaO) and/or zinc oxide (ZnO) may be present in the glasscompositions. The total amount of alkaline earth oxides and ZnO in theglass compositions may be RO (mol. %). The total amount of alkalineearth oxides without BeO and ZnO (i.e., RO (mol. %)-BeO(mol. %)-ZnO(mol.%)) may be A mol. %. Increasing the amount of Al₂O₃ in the glasscompositions improves ion exchange in the glass compositions. However,the liquidus temperature increases rapidly when Al₂O₃ (mol. %) exceeds(R₂O (mol. %)+RO (mol. %)) by more than 1 or 2 mol. %. BeO and ZnO maynot be as active as the other alkaline earth oxides and may not have asmuch impact on the ion exchange characteristics or liquidus temperatureas the other alkaline earth oxides. Therefore, the liquidus temperaturemay increase rapidly when Al₂O₃ (mol. %) exceeds (R₂O (mol. %)+A (mol.%)) as well. As the liquidus temperature of the glass increases, theliquidus viscosity of the glass decreases. If the amount of Al₂O₃ in theglass composition is too high, then the liquidus temperature increasesto the point that the glass is no longer fusion formable in a fusiondowndraw process due to devitrification in the glass. Devitrificationrefers to the crystallization of one or more constituents of the glasscomposition during formation (e.g., formation of cristobalite,spodumene, mullite, rutile, corundum, other crystalline constituent, orcombinations of these). Thus, in some embodiments, Al₂O₃ (mol. %) in theglass compositions may not exceed the sum (R₂O (mol. %)+RO (mol. %)) or(R₂O (mol. %)+A (mol. %)) by more than 10 mol. %. In some embodiments,Al₂O₃ (mol. %) does not exceed the sum (R₂O (mol. %)+RO (mol. %)) or(R₂O (mol. %)+A (mol. %)) by more than 5 mol. %, by more than 2 mol. %,or even by more than 1 mol. %. For example, the glass compositions mayhave (Al₂O₃ (mol. %)-R₂O (mol. %)-RO (mol. %)) that is less than orequal to 10 mol. %, less than or equal to 5 mol. %, less than or equalto 2 mol. %, or even less than or equal to 1 mol. %, where RO (mol. %)is the sum of the molar amounts of BeO, MgO, CaO, SrO, BaO, and ZnO. Insome embodiments, (Al₂O₃ (mol. %)-R₂O (mol. %)-RO (mol. %)) may begreater than 0 mol. % and less than or equal to 10 mol. %, greater than0 mol. % and less than or equal to 5 mol. %, greater than 0 mol. % andless than or equal to 2 mol. %, or even greater than 0 mol. % and lessthan or equal to 1 mol. %. In some embodiments, the glass compositionsmay be substantially free of phosphorous oxide (P₂O₅). In theseembodiments in which P₂O₅ is not present in the glass composition tocompensate for the excess Al₂O₃, the quantity (Al₂O₃ (mol. %)-R₂O (mol.%)-RO (mol. %)) may be less than or equal to 4 mol. %, less than orequal to 2 mol. %, or even less than or equal to 1 mol. % in the glasscompositions.

The glass compositions described herein generally include Al₂O₃ in anamount greater than or equal to about 2 mol. % and less than or equal toabout 25 mol. % or greater than or equal to about 7 mol. % and less thanor equal to about 25 mol. % and any ranges or subranges therebetween. Insome embodiments, the amount of Al₂O₃ in the glass compositions may begreater than or equal to about 10 mol. % and less than or equal to about18 mol. %. In some other embodiments, the amount of Al₂O₃ in the glasscompositions may be greater than or equal to about 12 mol. % to lessthan or equal to about 16 mol. %. In some other embodiments, the amountof Al₂O₃ in the glass compositions may be greater than or equal to about10 mol. % to less than or equal to about 16 mol. %. In still otherembodiments, the amount of Al₂O₃ in the glass compositions may begreater than or equal to about 12 mol. % to less than or equal to about18 mol. %.

The glass compositions also include one or more alkali oxides. Thealkali oxides facilitate the ion exchangeability of the glasscompositions and, as such, facilitate chemically strengthening theglass. The alkali oxides may include one or more of Li₂O, Na₂O, K₂O,Rb₂O, and Cs₂O. As previously discussed, the alkali oxides are generallypresent in the glass compositions in a total concentration of R₂O mol.%. Increasing the amount of alkali oxides improves ion exchange in theresultant glass. However, if the amount of alkali oxides is too high,such as higher than 14 mol. %, the liquidus viscosity of the glasscomposition decreases. When the liquidus viscosity decreases, loweringthe temperature of the molten glass compositions to increase theviscosity for fusion forming results in devitrification in the glasscompositions during forming. Therefore, in some embodiments, the glasscomposition may have less than or equal to 14 mol. % R₂O (mol. %). Insome embodiments, the glass composition may include greater than orequal to 7 (mol. %) and less than or equal to 14 (mol. %) R₂O.

The ion exchangeability of the glass formed from the glass compositionsdescribed herein is primarily imparted to the glass by the amount of thealkali oxide Li₂O initially present in the glass compositions prior toion exchange. Accordingly, in the embodiments of the glass compositionsdescribed herein, the alkali oxide present in the glass compositionsincludes at least Li₂O. Lithium ions are smaller than other alkali ions,such as sodium ions (Na⁺), potassium ions (K⁺), rubidium ions (Rb⁺), andcesium ions (Cs⁺) for example. When glasses formed from the glasscompositions comprising Li₂O are ion exchanged with sodium or potassiumions, the ion exchange of the larger sodium and/or potassium ions forthe smaller lithium ions occurs rapidly compared to ion exchange of thesodium and/or potassium ions with other sodium or potassium ions. Thus,a greater amount of Li₂O in the glass compositions relative to the otheralkali oxides results in better ion exchange performance of theresultant glass. For example, ion exchange of the lithium ions in theglass with sodium and/or potassium ions results in greater compressivestress and greater depth of the compressive layer of the glass comparedto ion exchange of other alkali ions in the glass with sodium and/orpotassium ions. When ion exchanging the glass with sodium ions, thegreater the amount of Li₂O in the glass relative to the other alkalioxides, the greater the compressive stress on the surface. Additionally,alkali oxides may create non-bridging oxygens in the glass network thatmay reduce chemical durability, decrease the viscosity, and slow downthe process of ion exchange. Therefore, in order to achieve the desiredcompressive strength and depth of layer in the glass upon ion exchangestrengthening, in embodiments, the molar ratio of the Li₂O to total R₂Oin the glass compositions is greater than or equal to 0.35, where R₂O isthe total molar amount of alkali oxides Li₂O, Na₂O, K₂O, Rb₂O, and Cs₂Oin the glass compositions (i.e., (Li₂O (mol. %))/(R₂O (mol. %)) isgreater than or equal to 0.35). If the molar ratio of Li₂O to R₂O in theglass composition is less than 0.35, the compressive stress resultingfrom ion exchange is reduced resulting in a weaker glass and decreaseddrop performance of the glass. In some embodiments, the molar ratio ofLi₂O to R₂O in the glass compositions may be greater than or equal to0.4, greater than or equal to 0.5, greater than or equal to 0.6, greaterthan or equal to 0.7, or even greater than or equal to 0.8.

Specifically, in order to achieve the desired compressive stress anddepth of compression in the glass upon ion exchange strengthening, inembodiments, the glass compositions include Li₂O in an amount from about2 mol. % to about 15 mol. % or from about 2 mol. % to about 14 mol. %and all ranges and subranges therebetween. If the amount of Li₂O in theglass compositions is too low, such as less than 2 mol. % for example,the rate of ion exchange in the glass decreases and the compressivestress in the glass created by ion exchange also decreases. If theamount of Li₂O in the glass compositions is too high, such as greaterthan 14 mol. % or 15 mol. % for example, the liquidus viscosity of theglass compositions decreases and the glass may crystallize during fusionforming. In some embodiments, the glass compositions include at leastabout 4 mol. % Li₂O. For example, the concentration of Li₂O in the glasscompositions may be greater than 5 mol. %, or greater than 6 mol. %. Insome embodiments, the glass compositions may have greater than or equalto 4 mol. % Li₂O, greater than or equal to 5 mol. % Li₂O, or evengreater than or equal to 6 mol. % Li₂O. In some embodiments, the glasscompositions include less than about 12 mol. % Li₂O, less than about 10mol. % Li₂O, or even less than about 9 mol. % Li₂O. In some embodiments,the glass compositions may have less than or equal to 14 mol. % Li₂O,less than or equal to 12 mol. % Li₂O, less than or equal to 10 mol. %Li₂O, or even less than or equal to 9 mol. % Li₂O. For example, in someembodiments the glass compositions may include greater than or equal to2 mol. % and less than or equal to 14 mol. % Li₂O, greater than or equalto 4 mol. % and less than or equal to 12 mol. % Li₂O, greater than orequal to 5 mol. % and less than or equal to 10 mol. % Li₂O, or evengreater than or equal to 6 mol. % and less than or equal to 9 mol. %Li₂O.

As noted above, the alkali oxide in the glass compositions may furtherinclude Na₂O. The amount of Na₂O present in the glass compositions alsorelates to the ion exchangeability of the glass made from the glasscompositions. Specifically, the presence of Na₂O in the glasscompositions may increase the ion exchange rate during ion exchangestrengthening of the glass by increasing the diffusivity of ions throughthe glass matrix. However, as the amount of Na₂O present in the glasscompositions increases, the compressive stress obtainable in the glassthrough ion exchange decreases as a result of the exchange of the sodiumions with other sodium ions. For example, ion exchange of a sodium ionwith another sodium ion of the same size results in no net increase inthe compressive stress in the compressive layer. Thus, increasing theNa₂O amount in the glass compositions decreases the compressive stresscreated in the glass by the ion exchange. Accordingly, it is desirableto limit the amount of Na₂O present in the glass compositions. In someembodiments, the amount of Na₂O is greater than or equal to 0 mol. % andless than or equal to 6 mol. % and all ranges and subrangestherebetween. In some embodiments, the glass compositions include atleast about 0.1 mol. % of Na₂O. For example, the glass compositions mayhave greater than or equal to 0.1 mol. % Na₂O, greater or equal to 0.2mol. % Na₂O, greater than or equal to 0.3 mol. % Na₂O, greater than orequal to 0.5 mol. % Na₂O, greater than or equal to 1 mol. % Na₂O, oreven greater than or equal to 1.5 mol. % Na₂O. In some embodiments, theglass compositions may include less than or equal to 6 mol. % Na₂O, lessor equal to 5 mol. % Na₂O, or even less than or equal to about 4 mol. %Na₂O. For example, in some embodiments the glass compositions mayinclude greater than or equal to 0 mol. % and less than or equal to 6mol. % Na₂O, greater than or equal to 0.1 mol. % and less than or equalto 6 mol. % Na₂O, greater than or equal to 0.2 mol. % and less than orequal to 5 mol. % Na₂O, greater than or equal to 0.3 mol. % and lessthan or equal to 4 mol. % Na₂O, greater than or equal to 0.5 mol. % andless than or equal to 6 mol. % Na₂O, greater than or equal to 1 mol. %and less than or equal to 6 mol. % Na₂O, or greater than or equal to 1.5mol. % and less than or equal to 6 mol. % Na₂O. Accordingly, it shouldbe understood that Na₂O need not be present in the glass compositions.However, when Na₂O is included in the glass compositions, the amount ofNa₂O in the glass compositions is generally less than about 6 mol. %.

As noted above, the alkali oxide in the glass compositions may furtherinclude K₂O. The amount of K₂O present in the glass compositions alsorelates to the ion exchangeability of the glass composition.Specifically, as the amount of K₂O present in the glass compositionsincreases, the compressive stress in the glass obtainable through ionexchange decreases as a result of the exchange of potassium and sodiumions. Accordingly, it is desirable to limit the amount of K₂O present inthe glass compositions. In some embodiments, the amount of K₂O in theglass compositions is greater than or equal to 0 mol. % and less than orequal to 2.5 mol. % and all ranges and subranges therebetween. In someembodiments, the amount of K₂O in the glass compositions is less orequal to 1 mol. % or even less than or equal to 0.25 mol. %. Inembodiments, the glass compositions may include greater than or equal toabout 0.01 mol. % and less than or equal to about 2.5 mol. % K₂O,greater than or equal to about 0.01 mol. % and less than or equal toabout 1 mol. % K₂O, or even greater than or equal to about 0.01 mol. %and less than or equal to about 0.25 mol. % K₂O. Accordingly, it shouldbe understood that K₂O need not be present in the glass compositions.However, when K₂O is included in the glass compositions, the amount ofK₂O is generally less than about 2.5 mol. %.

The glass compositions may also include phosphorous oxide (P₂O₅). Thepresence of P₂O₅ increases the liquidus viscosity of the glasscompositions by suppressing the crystallization of mullite in the glasscompositions. The liquidus temperature of the glass compositionsincreases rapidly when the amount of Al₂O₃ exceeds the sum of theamounts of alkali oxides (R₂O mol. %) and alkaline earth oxides (RO mol.%) in the glass composition by more than 2 mol. %, or even by more than1 mol. %. When Al₂O₃ (mol. %) is greater than (R₂O (mol. %)+RO (mol. %))by more than 1 mol. %, the presence of P₂O₅ in the glass compositioncompensates for the excess Al₂O₃ by decreasing the liquidus temperature,thus, increasing the liquidus viscosity of the glass composition. Insome embodiments, the glass compositions may have an amount of P₂O₅sufficient to compensate for the excess Al₂O₃. For example, in someembodiments, the glass compositions may have an amount of P₂O₅sufficient so that (Al₂O₃ (mol. %)-R₂O (mol. %)-RO (mol. %)-P₂O₅ (mol.%)) is less than or equal to 2 or even less than or equal to 1. In someembodiments, the glass compositions may have an amount of P₂O₅ so that(Al₂O₃ (mol. %)-R₂O (mol. %)-RO (mol. %)-P₂O₅ (mol. %)) is greater thanor equal to −2 or even greater than or equal to −1. In some embodiments,the glass compositions may have an amount of P₂O₅ sufficient so that(Al₂O₃ (mol. %)-R₂O (mol. %)-RO (mol. %)-P₂O₅ (mol. %)) is greater thanor equal to −2 and less than or equal to 2, or even greater than orequal to −1 and less than or equal to 1. In some embodiments, thepresence of P₂O₅ also achieves the effects noted above, when the ratioof P₂O₅ (mol %)/[(Al₂O₃—R₂O—RO)](mol %) is in a range from 0.25 to 1.5,from 0.25 to 1.4, from 0.25 to 1.3, from 0.25 to 1.25, from 0.25 to 1.2,from 0.25 to 1.1, from 0.25 to 1, from 0.25 to 0.9, from 0.25 to 0.8,from 0.25 to 0.7, from 0.25 to 0.6, from 0.5 to 1.5, from 0.5 to 1.4,from 0.5 to 1.3, from 0.5 to 1.25, from 0.5 to 1.2, from 0.5 to 1.1,from 0.5 to 1, from 0.5 to 0.9, from 0.5 to 0.8, from 0.5 to 0.7, from0.5 to 0.6, from 0.6 to 1.5, from 0.6 to 1.4, from 0.6 to 1.3, from 0.6to 1.25, from 0.6 to 1.2, from 0.6 to 1.1, from 0.6 to 1, from 0.6 to0.9, from 0.6 to 0.8, from 0.6 to 0.7, from 0.7 to 1.5, from 0.7 to 1.4,from 0.7 to 1.3, from 0.7 to 1.25, from 0.7 to 1.2, from 0.7 to 1.1,from 0.7 to 1, from 0.7 to 0.9, from 0.7 to 0.8, from 0.8 to 1.5, from0.8 to 1.4, from 0.8 to 1.3, from 0.8 to 1.25, from 0.8 to 1.2, from 0.8to 1.1, from 0.8 to 1, from 0.8 to 0.9, from 0.9 to 1.5, from 0.9 to1.4, from 0.9 to 1.3, from 0.9 to 1.25, from 0.9 to 1.2, from 0.9 to1.1, or from 0.9 to 1, and all ranges and subranges therebetween. Insome embodiments, the glass compositions do not include P₂O₅, and aspreviously described, in the absence of the P₂O₅, the glass compositionshave (Al₂O₃ (mol. %)-R₂O (mol. %)-RO (mol. %)) that is greater than orequal to 0 and less than or equal to 2, or even greater than or equal to0 and less than or equal to 1.

The amount of P₂O₅ also relates to the ion exchangeability of the glassmade from the glass composition. Increasing the amount of P₂O₅ in theglass compositions may increase the rate of ion exchange in the glass bycreating space within the glass network. P₂O₅ may also contribute toenhancing the damage resistance of the glass made from the glasscompositions. However, increasing the amount of P₂O₅ in the glasscompositions decreases the amount of compressive stress attainablethrough ion exchange strengthening of the glass. Additionally,increasing the amount of P₂O₅ too high may cause crystallization ofaluminum phosphate (AlPO₄) at high temperatures, which may increase theliquidus temperature of the class compositions. If the amount of P₂O₅ inthe glass compositions is too high, then the durability of the glass mayalso be reduced. Therefore, the total amount of P₂O₅ in the glasscomposition may be limited, such as less than or equal to 20 mol. % forexample. In some embodiments, the glass compositions include P₂O₅ in anamount from about 0.1 mol. % to about 20 mol. % and all ranges andsubranges therebetween. For example, the amount of P₂O₅ in the glasscompositions may be greater than about 0.4 mol. %, greater than about 1mol. %, greater than about 3 mol. %, or even greater than about 3.5 mol.%. In some embodiments, the glass compositions may have greater than orequal to 0.1 mol. % P₂O₅, greater than or equal to 0.4 mol. % P₂O₅,greater than or equal to 1 mol. % P₂O₅, greater than or equal to 3 mol.% P₂O₅, or even greater than or equal to 3.5 mol. % P₂O₅. In someembodiments, the glass compositions may include less than about 20 mol.% P₂O₅, less than about 10 mol. % P₂O₅, less than about 8 mol. % P₂O₅,less than about 6 mol. % P₂O₅, or even less than about 5.5 mol. % P₂O₅.In some embodiments, the glass compositions may have less than or equalto 20 mol. % P₂O₅, less than or equal to 10 mol. % P₂O₅, less than orequal to 8 mol. % P₂O₅, less than or equal to 6 mol. % P₂O₅, or evenless than or equal to 5.5 mol. % P₂O₅. For example, in some embodimentsthe glass compositions may include greater than or equal to 0.1 mol. %and less than or equal to 20 mol. % P₂O₅, greater than or equal to 0.4mol. % and less than or equal to 10 mol. % P₂O₅, greater than or equalto 1 mol. % and less than or equal to 8 mol. % P₂O₅, greater than orequal to 3 mol. % and less than or equal to 6 mol. % P₂O₅, or evengreater than or equal to 3.5 mol. % and less than or equal to 5.5 mol. %P₂O₅. Accordingly, it should be understood that P₂O₅ need not be presentin the glass compositions. However, when P₂O₅ is included in the glasscompositions, the amount of P₂O₅ in the glass compositions is generallyless than about 20 mol. %.

Boron oxide (B₂O₃) is a flux which may be added to glass compositions toreduce the viscosity of the glass at a given temperature (e.g., thetemperature corresponding to the viscosity of 200 poise, at which glassis melted and which is usually the highest temperature in the glassmelting furnace.) thereby improving the quality and formability of theglass. The presence of B₂O₃ may also improve damage resistance of theglass made from the glass composition. However, it has been found thatadditions of B₂O₃ significantly decrease the diffusivity of sodium andpotassium ions in the glass compositions, which, in turn, adverselyimpacts the ion exchange performance of the resultant glass. Inparticular, it has been found that additions of B₂O₃ may increase thetime required to achieve a given depth of layer in the glass relative toglass compositions which are boron free. The addition of B₂O₃ may alsoincrease the temperature at which ion exchange is conducted in order toachieve an ion exchange rate necessary to reach a target depth of layerin the glass in a given duration of time.

The effect of B₂O₃ on ion exchange performance of the glass may becompensated for by adding greater amounts of Li₂O and Al₂O₃ to the glasscomposition, which may compensate for the presence of B₂O₃ in the glasscomposition. For example, it has been determined that the impact of B₂O₃on the ion exchange performance of a glass can be mitigated bycontrolling the ratio of the amount of B₂O₃ to the sum of the amounts ofLi₂O and Al₂O₃ in the glass composition. In particular, it has beendetermined that when the sum of (Li₂O (mol. %)+Al₂O₃ (mol. %)) isgreater than two times the amount of B₂O₃ (mol. %) in the glasscomposition, the diffusivities of alkali oxides in the resultant glassare not diminished and, as such, the ion exchange performance of theglass is maintained. Accordingly, in some embodiments, the ratio of(Li₂O (mol. %)+Al₂O₃ (mol. %))/(B₂O₃ (mol. %)) in the glass compositionis greater than or equal to 2. At ratios of (Li₂O (mol. %)+Al₂O₃ (mol.%))/(B₂O₃ (mol. %)) in the glass composition less than 2, thediffusivities of the alkali oxides in the glass composition decrease andthe ion exchange performance also decreases.

In the embodiments described herein, the amount of B₂O₃ in the glasscompositions may be from about 0.1 mol. % to about 20 mol. % and allranges and subranges therebetween. For example, the amount of B₂O₃ inthe glass compositions may be greater than about 0.1 mol. %, greaterthan about 3 mol. %, or even greater than about 4 mol. %. In someembodiments, the glass compositions may have greater than or equal to0.1 mol. % B₂O₃, greater than or equal to 3 mol. % B₂O₃, or even greaterthan or equal to 4 mol. % B₂O₃. In some embodiments, the glasscompositions include less than about 20 mol. % B₂O₃, less than about 15mol. % B₂O₃, less than about 10 mol. % B₂O₃, or even less than about 7mol. % B₂O₃. In some embodiments, the glass compositions may includeless than or equal to 20 mol. % B₂O₃, less than or equal to 15 mol. %B₂O₃, less than or equal to 10 mol. % B₂O₃, or even less than or equalto 7 mol. % B₂O₃. For example, in some embodiments, the glasscompositions may include greater than or equal to 0.1 mol. % and lessthan or equal to 20 mol. % B₂O₃, greater than or equal to 3 mol. % andless than or equal to 15 mol. % B₂O₃, greater than or equal to 4 mol. %and less than or equal to 10 mol. % B₂O₃, or even greater than or equalto 4 mol. % and less than or equal to 7 mol. % B₂O₃. Accordingly, itshould be understood that B₂O₃ need not be present in the glasscompositions. However, when B₂O₃ is included in the glass compositions,the amount of B₂O₃ in the glass composition is generally less than about20 mol. %.

Alkaline earth oxides may be present in the glass compositions toimprove the meltability of the glass batch materials and increase thechemical durability of the resultant glass. In particular, the presenceof small amounts of alkaline earth oxides may work to increase theliquidus viscosity of the glass composition. However, too much alkalineearth oxide in the glass composition cause crystallization ofaluminosilicates and, therefore, reduce the liquidus viscosity of theglass compositions. The presence of alkaline earth oxides may alsoimpact the ion exchange performance of the resultant glass. For example,in the glass compositions described herein, the total amount (in mol. %)of alkaline earth oxides (i.e., RO (mol. %)) present in the glasscompositions is generally less than the total amount in mol. % of alkalioxides present in the glass compositions (i.e., R₂O (mol. %)) in orderto improve the ion exchangeability of the glass. In the embodimentsdescribed herein, the glass compositions generally include from about 0mol. % to about 5 mol. % alkaline earth oxides and all ranges andsubranges therebetween. In some of these embodiments, the amount ofalkaline earth oxides in the glass composition may be from about 0 mol.% to about 3 mol. % or even from about 0 mol. % to about 2 mol. %.

The alkaline earth oxides in the glass composition may include BeO, MgO,CaO, SrO, BaO, or combinations thereof. In some embodiments, the glasscomposition may be free or substantially free of BaO. In someembodiments, the alkaline earth oxides may include BeO, MgO, CaO, SrO,or combinations thereof. For example, in the embodiments describedherein the alkaline earth oxides may include MgO. In embodiments, theglass compositions may include greater than or equal to about 0 mol. %and less than or equal to about 5 mol. % MgO and all ranges andsubranges therebetween. In some embodiments, the glass compositions mayinclude greater than 0 mol. % MgO. In some embodiments, glasscompositions may include greater than 0 mol. % and less than or equal toabout 5 mol. % MgO, greater than 0 mol. % and less than or equal to 3mol. % MgO, or even greater than 0 mol. % and less than or equal to 0.2mol. % MgO. Accordingly, it should be understood that MgO need not bepresent in the glass compositions. However, when MgO is included in theglass compositions, the amount of MgO in the glass compositions isgenerally less than about 5 mol. %.

In some embodiments, the alkaline earth oxides may further optionallyinclude CaO. The presence of CaO may increase the liquidus viscosity ofthe glass compositions. However, too much CaO in the glass compositionmay decrease the rate of ion exchange in the resultant glass. Inembodiments, CaO may be present in the glass composition in an amountfrom about 0 mol. % to about 4 mol. % and all ranges and subrangestherebetween. For example, the amount of CaO present in the glasscomposition may be less than or equal to 4 mol. %, less than or equal to2 mol. %, or even less than or equal to 1 mol. %. In some embodiments,the glass composition may include greater than 0 mol. % CaO. In some ofthese embodiments, the glass composition may include greater than 0 mol.% and less than or equal to about 4 mol. % CaO. For example, the glasscomposition may include greater than 0 mol. % and less than or equal toabout 2 mol. % CaO or even greater than 0 mol. % and less than or equalto about 1 mol. % CaO. Accordingly, it should be understood that CaOneed not be present in the glass compositions. However, when CaO isincluded in the glass compositions, the amount of CaO in the glasscompositions is generally less than about 4 mol. %.

In some embodiments, the alkaline earth oxides may further optionallyinclude SrO. The presence of SrO may act to increase the liquidusviscosity of the glass composition, However, too much SrO in the glasscomposition may decrease the rate of ion exchange in the resultantglass. In embodiments, SrO may be present in the glass composition in anamount from about 0 mol. % to less than or equal to 4 mol. % and allranges and subranges therebetween. For example, the amount of SrOpresent in the glass composition may be less than or equal to 4 mol. %,less than or equal to 2 mol. %, or even less than or equal to 1 mol. %.In some embodiments, the glass composition may include greater than 0mol. % SrO. In some of these embodiments, the glass composition mayinclude greater than 0 mol. % and less than or equal to about 4 mol. %SrO. For example, the glass composition may include greater than 0 mol.% and less than or equal to about 2 mol. % SrO or even greater than 0mol. % and less than or equal to about 1 mol. % SrO. Accordingly, itshould be understood that SrO need not be present in the glasscompositions. However, when SrO is included in the glass compositions,the amount of SrO in the glass compositions is generally less than about4 mol. %.

In addition to the SiO₂, Al₂O₃, P₂O₅, B₂O₃, alkali oxides, and alkalineearth oxides, the glass compositions described herein may optionallyfurther include one or more fining agents such as, for example, SnO₂,As₂O₃, and/or (from NaCl or the like). The fining agents may be includedin the glass composition to minimize or eliminate bubbles in the glasscomposition during formation. However, the fining agents generally havelow solubility in the glass composition. Thus, if the amount of finingagents in the glass composition is too great, devitrification of thefining agents may occur during fusion forming. When a fining agent ispresent in the glass composition, the fining agent may be present in anamount less than or equal to 0.35 mol. %, less than or equal to 0.2 mol.%, or even less than or equal to 0.1 mol. %. For example, in someembodiments the glass composition may include SnO₂ as a fining agent. Inthese embodiments, the glass compositions may include greater than orequal to 0 mol. % and less than or equal to 0.35 mol. % SnO₂, greaterthan 0 mol. % and less than or equal to about 0.2 mol. % SnO₂, an amountgreater than 0 mol. % and less than or equal to 0.1 mol. % SnO₂, or evenan amount greater than or equal to about 0.01 mol. % and less than orequal to about 0.05 mol. % SnO₂. Accordingly, it should be understoodthat SnO₂ or other fining agents need not be present in the glasscompositions. However, when SnO₂ or other fining agents are included inthe glass compositions, the total amount of SnO₂ and other fining agentsin the glass compositions is generally less than about 0.35 mol. %.

Moreover, the glass compositions described herein may comprise one ormore additional metal oxides to further improve the chemical durabilityof the resultant glass. For example, the glass composition may furtheroptionally include transition metal oxides such as ZnO, TiO₂, ZrO₂, orcombinations of these. Each of these metal oxides may further improvethe resistance of the glass to chemical attack. However, theseadditional metal oxides are not very soluble in the glass compositionsand tend to crystallize, resulting in devitrification during fusionforming. In these embodiments, the additional metal oxides may bepresent in an amount which is greater than or equal to about 0 mol. %and less than or equal to about 5 mol. % and all ranges and subrangestherebetween. For example, when the additional metal oxide is ZnO, theZnO may be present in an amount greater than or equal to 0 mol. % andless than or equal to about 5 mol. %, greater than or equal to 0 mol. %and less than or equal to 3 mol. %, or even greater than or equal to 0mol. % and less than or equal to 2 mol. %. In some embodiments, when theadditional metal oxide is ZrO₂ or TiO₂, the ZrO₂ or TiO₂ may be presentin an amount less than or equal to about 1 mol. %. Accordingly, itshould be understood that these additional metal oxides need not bepresent in the glass composition. However, when ZnO, ZrO₂, or TiO₂ areincluded in the glass composition, the total amount of the ZnO, ZrO₂,and TiO₂ in the glass composition is generally less than about 5 mol. %.

In some embodiments, the glass compositions may include one or more rareearth metal oxides. Rare earth metals refer to the metals listed in theLanthanide Series of the IUPAC Periodic Table plus yttrium and scandium.The presence of rare earth metal oxides in the glass composition mayincrease the modulus, stiffness, or modulus and stiffness of theresultant glass. Rare earth metal oxides may also help to increase theliquidus viscosity of the glass composition. Additionally, certain rareearth metal oxides may add color to the glass. If no color is requiredor desired, then the glass composition may include lanthanum oxide(La₂O₃), yttrium oxide (Y₂O₃), gadolinium oxide (Gd₂O₃), ytterbium oxide(Yb₂O₃), lutelium oxide (Lu₂O₃), or combinations of these. For colorlessglasses, the rare earth metal oxides may include Ce₂O₃, Pr₂O₃, Nd₂O₃,Sm₂O₃, Eu₂O₃, Tb₂O₃, Dy₂O₃, Ho₂O₃, Er₂O₃, Tm₂O₃, or combinations ofthese. In embodiments, the glass compositions may include a total amountof rare earth metal oxides of from 0 mol. % to 4 mol. % and all rangesand subranges therebetween. For example, the glass compositions mayinclude greater than 0 mol. % and less than or equal to 4 mol. % rareearth metal oxides, greater than 0 mol. % and less than or equal to 2mol. % rare earth metal oxides, greater than 0 mol. % and less than orequal to 1.5 mol. % rare earth metal oxides, greater than 0 mol. % andless than or equal to 1 mol. % rare earth metal oxides, greater than 0mol % and less than or equal to 0.5 mol % rare earth metal oxides, lessthan 4 mol. % rare earth metal oxides, less than 3 mol. % rare earthmetal oxides, less than 2 mol. % rare earth metal oxides, less than 1mol. % rare earth metal oxides, or less than 0.5 mol % rare earth metaloxides. In some embodiments, the rare earth metal oxide may includeLa₂O₃. For example, in some embodiments, the glass compositions mayinclude greater than 0 mol. % and less than or equal to 4 mol. % La₂O₃.Accordingly, it should be understood that rare earth metal oxides neednot be present in the glass compositions. However, when rare earth metaloxides are included in the glass compositions, the total amount of rareearth metal oxides in the glass compositions is generally less thanabout 4 mol. %.

The glass compositions may include less than 0.05 mol. % trampcompounds, such as manganese compounds, cerium compounds, halfniumcompounds, or other compounds, that may make it into the glasscomposition as impurities in the SiO₂, Al₂O₃, Li₂O, P₂O₅, B₂O₃, alkalimetal oxides, alkaline metal oxides, other metal oxide, or otherintentionally included constituents of the glass composition. Trampcompounds may also enter the glass composition through contact withprocessing equipment, such as refractory components of a fusion downdrawforming process, or the like.

As discussed below, the glass compositions described herein can bechemically strengthened through ion exchange to impart a compressivestress at the surface of a glass article. However, during the ionexchange process, the compressive stress formed near the glass surfacemay decrease as a result of a process known as stress relaxation, whichis governed by the viscosity of the glass wherein the lower theviscosity of the glass, the faster the stresses relax and the lessefficient the process of chemical strengthening. In some embodiments,the composition of the glass can be controlled to minimize the effect ofstress relaxation. The glasses can be characterized by a quantity Awhich is an estimate of the logarithm of viscosity (in Poises) at atemperature equal to 400° C., which is close to most typicaltemperatures for ion exchange, wherein:

A=13.2+P*[(1/673−1(A.P.+273))]

wherein P=0.6/[(1/(A.P.+273))−(1/(T ₁₂+273))],

wherein A.P. is the annealing point in ° C., and

wherein T₁₂ is the temperature corresponding to when the glass has aviscosity of 10¹² Poises.

In some embodiments, when A is greater than or equal to 17, greater thanor equal to 18, greater than or equal to 19, or greater than or equal to20, stress relaxation is minimized.

The glass compositions described herein are formed by mixing a batch ofglass raw materials (e.g., powders of spodumene, sand, aluminum oxide,aluminum metaphosphate, boric acid, alkali carbonates, alkali nitrates,alkaline earth carbonates, alkaline earth oxides and the like) such thatthe batch of glass raw materials has the desired composition.Thereafter, the batch of glass raw materials is heated to form a moltenglass composition which is subsequently cooled and solidified to formthe glass composition. During solidification (i.e., when the glasscomposition is plastically deformable) the glass composition may beshaped using standard forming techniques to shape the glass compositioninto a desired final form. Alternatively, the glass article may beshaped into a stock form, such as a sheet, ribbon, tube or the like, andsubsequently reheated and formed into the desired final form.

The glass compositions described herein may be shaped into glassarticles having various forms such as, for example, sheets, ribbons,tubes, or the like. However, given the mechanical durability, the glasscompositions described herein are particularly well suited for use inthe formation of cover glass for electronic devices, such as portableelectronic devices. Moreover, the ability to chemically strengthen theglass compositions through ion exchange can be utilized to furtherimprove the mechanical durability of the glass sheets and articles madefrom the glass compositions disclosed herein. Accordingly, it should beunderstood that, in at least one embodiment, the glass compositions areincorporated in an electronic device to improve the mechanicaldurability of the electronic device.

The fusion downdraw process is one technique for shaping the moltenglass compositions described herein into glass sheets and glass ribbonsduring solidification of the glass compositions. The fusion downdrawprocess produces glass sheets and ribbons with relatively low amounts ofdefects and with surfaces having superior flatness, compared to ribbonsmade using other glass ribbon forming processes, such as the float andslot-draw processes. As a result, fusion downdraw processes are widelyemployed for the production of glass substrates used in the manufactureof LED and LCD displays and other substrates that require superiorflatness. In a typical fusion downdraw process, the glass composition isprepared and melted, and the molten glass composition is fed into aforming body (also referred to as an isopipe), which includes formingsurfaces that converge at a root. The molten glass flows evenly over theforming surfaces of the forming body and forms a ribbon of flat glasswith pristine surfaces. The ribbon of flat glass is drawn away from theroot of the forming body at a rate greater than the rate at which theglass flows downward along the forming surfaces of the forming bodyunder gravity. The viscosities of the glass compositions generallydecrease exponentially with increasing temperature. Therefore, the glasscompositions may have a liquidus temperature as low as possible toincrease the viscosity of the glass composition at the liquidustemperature (i.e., the liquidus viscosity). This ensures that the rateat which the glass ribbon is drawn away from the root is greater thanthe rate at which the glass composition flows down the forming surfacesof the forming body. If the liquidus temperature of the glasscomposition is too high, then the liquidus viscosity becomes too low toeffectively downdraw the glass composition. Decreasing the temperaturebelow the liquidus temperature to reduce the viscosity of the glasscomposition causes devitrification of the glass composition duringfusion forming process. Devitrification of constituents of the glasscomposition during fusion forming results in flaws and/or imperfectionsin the glass ribbon, in particular in the surface of the glass ribbon.Additionally, crystallization of constituents also diminishes theformability of the glass.

As previously described, the glass compositions disclosed herein have aliquidus temperature that is low enough so that the liquidus viscosityof the glass composition is sufficiently high to enable the glasscomposition to be formed by a fusion downdraw forming process. Forexample, in some embodiments, the glass compositions may have a liquidustemperature of less than or equal to 1300° C. In other embodiments, theglass compositions may have liquidus temperatures of less than or equalto 1250° C., less than or equal to 1200° C., or even less than or equalto 1150° C. In some embodiments, the glass compositions may have aliquidus temperature of greater than or equal to 1100° C. and less thanor equal to 1300° C., greater than or equal to 1100° C. and less than orequal to 1250° C., greater than or equal to 1150° C. and less than orequal to 1300° C., or greater than or equal to 1150° C. and less than orequal to 1250° C. In embodiments, the glass compositions have a liquidusviscosity sufficient to enable the glass composition to be formed usinga fusion downdraw forming process. For example, in some embodiments, theglass compositions may have a high liquidus viscosity of at least 20kilopoise (kP) (20,000 poise (P) or 2000 Pascal seconds (Pa-s), where 1kP is equal to 100 Pascal seconds (Pa-s). In other embodiments, theglass compositions may have a liquidus viscosity of at least 50 kP, atleast 100 kP, at least 200 kP, at least 300 kP, or even at least 500 kP.In some embodiments, the glass compositions may have a liquidusviscosity of greater than or equal to 20 kP, greater than or equal to 50kP, greater than or equal to 100 kP, greater than or equal to 200 kP,greater than or equal to 300 kP, greater than or equal to 500 kP, oreven greater than or equal to 1000 kP. In other embodiments, the glasscompositions may have a liquidus viscosity less than about 1200 kP, oreven less than 1000 kP. In still other embodiments, the glasscomposition may have a liquidus viscosity of greater than or equal to 20kP and less than or equal to 1000 kP. For example, the glasscompositions may have a liquidus viscosity of greater than or equal to50 kP and less than or equal to 1000 kP, greater than or equal to 100 kPand less than or equal to 1000 kP, or even greater than or equal to 500kP and less than or equal to 1000 kP.

As discussed, the glass compositions disclosed herein have liquidusviscosities sufficiently high to enable forming, such as forming intoglass ribbons and/or sheets, using fusion downdraw forming processes.However, the glass compositions may also be made using other known glassforming methods, such as float methods or slot draw processes, forexample. In float methods, the molten glass composition is floated ontop of a bath of a molten metal bath, such as a molten tin bath. Themolten glass composition cools as it passes along the surface of themolten metal until the glass is removed from the surface of the bath asa glass ribbon formed from the glass composition. Other glass formationprocesses are also contemplated.

Glass articles and glass sheets made from the glass compositionsdescribed herein may be chemically strengthened by ion exchange. In theion exchange strengthening process, ions in the surface layer of theglass made from the glass compositions are replaced by—or exchangedwith—larger ions having the same valence or oxidation state. Inembodiments, ions in the surface layer of the glass composition and thelarger ions are monovalent alkali metal cations, such as Li⁺, Na⁺, Rb⁺,and Cs⁺. Alternatively, monovalent cations in the surface layer may bereplaced with monovalent cations other than alkali metal cations, suchas Ag⁺ or the like.

Commercial-scale ion exchange processes are typically carried out byimmersing a glass article or glass sheet made from the glass compositionin a molten salt bath containing the larger ions to be exchanged withthe smaller ions in the glass composition. It will be appreciated bythose skilled in the art that parameters for the ion exchange process,including, but not limited to, bath composition and temperature,immersion time, the number of immersions of the glass in a salt bath (orbaths), use of multiple salt baths, additional steps such as annealing,washing, and the like, are generally determined by the glass compositionand the desired depth of layer and compressive stress of the glasscomposition that result from the ion exchange strengthening process. Byway of example, ion exchange of alkali metal-containing glasses may beachieved by immersion in at least one molten bath containing a salt suchas, but not limited to, nitrates, sulfates, and chlorides, of the largeralkali metal ion. The temperature of the molten salt bath typically isin a range from about 350 degrees Celsius (° C.) up to about 450° C.,while immersion times range from about 0.1 hours up to about 36 hours.However, temperatures and immersion times different from those describedabove may also be used.

Ion exchange strengthening creates compressive stress in the outerregions of the glass made from the glass composition by replacing aplurality of first alkali metal ions in the outer region of the glasswith a plurality of second metal ions from the molten salt bath so thatthe outer region comprises the plurality of the second metal ions. Eachof the first alkali metal ions has a first ionic radius and each of thesecond metal ions has a second ionic radius. The second ionic radius isgreater than the first ionic radius, and the presence of the largersecond metal ions in the outer region creates the compressive stress inthe outer region. The first alkali metal ions may be ions of lithium,sodium, potassium, or rubidium. The second metal ions may be ions of atleast one of sodium, potassium, rubidium, and cesium. Generally, thesecond metal ion is different than the first alkali metal ion and has anionic radius greater than the ionic radius of the first alkali metalion.

Compressive stress (CS), depth of compression (DOC), and depth of layer(DOL) of a particular ion resulting from ion exchange may be measuredusing known techniques. Compressive stress (including surface CS) ismeasured by surface stress meter (FSM) using commercially availableinstruments such as the FSM-6000, manufactured by Orihara IndustrialCo., Ltd. (Japan). Surface stress measurements rely upon the accuratemeasurement of the stress optical coefficient (SOC), which is related tothe birefringence of the glass. SOC in turn is measured according toProcedure C (Glass Disc Method) described in ASTM standard C770-16,entitled “Standard Test Method for Measurement of Glass Stress-OpticalCoefficient.”

As used herein, DOC means the depth at which the stress in thechemically strengthened alkali aluminosilicate glass article describedherein changes from compressive to tensile. DOC may be measured by FSMor a scattered light polariscope (SCALP) depending on the ion exchangetreatment. Where the stress in the glass article is generated byexchanging potassium ions into the glass article, FSM is used to measureDOC. Where the stress is generated by exchanging sodium ions into theglass article, SCALP is used to measure DOC. Where the stress in theglass article is generated by exchanging both potassium and sodium ionsinto the glass, the DOC is measured by SCALP, since it is believed theexchange depth of sodium indicates the DOC and the exchange depth oflayer potassium ions (Potassium DOL or K DOL) indicates a change in themagnitude of the compressive stress (but not the change in stress fromcompressive to tensile); the exchange depth of potassium ions in suchglass articles is measured by FSM.

The DOC values disclosed herein, specifically the DOC values of at least10% of the thickness of the glass, and more preferably greater than orequal to 20% of the thickness of the glass, reflect DOC values computedusing the SCALP technique. For clarity, the DOC value represents thethickness of at least one compression stress layer, which means that thestrengthened glass article or sheet may have one compression layer witha DOC of at least 20% of the thickness of the glass or two compressionlayers with each having a DOC of at least 20% of the thickness of theglass. The disclosed DOC values are not a combination, for example, asum or average, of the two compressive stress layers.

As noted above, the presence of alkali oxides in the glass compositionfacilitates chemically strengthening the resultant glass by ionexchange. Specifically, alkali ions, such as lithium ions, sodium ions,potassium ions, and the like, are sufficiently mobile in the glasscomposition to facilitate ion exchange. In some embodiments, the glassmay be ion exchanged by introducing the glass, such as a glass articleor glass sheet made from the glass composition for example, into an ionexchange bath (e.g., immersing the glass in the ion exchange bath)comprising sodium nitrate (NaNO₃), potassium nitrate (KNO₃), or both. Inembodiments, the ion exchange bath may include from 1 weight percent(wt. %) to 100 wt. % NaNO₃, based on the total weight of the ionexchange bath. For example, the ion exchange bath may include from 1 wt.% to 99 wt. %, from 1 wt. % to 80 wt. %, from 1 wt. % to 20 wt. %, from20 wt. % to 100 wt. %, from 20 wt. % to 99 wt. %, from 20 wt. % to 80wt. %, from 80 wt. % to 100 wt. %, or from 80 wt. % to 99 wt. % NaNO₃,based on the total weight of the ion exchange bath. The ion exchangebath may also include an amount of KNO₃ sufficient to increase thecompressive stress at the surface of the glass. For example, inembodiments, the ion exchange bath may include from 0 wt. % to 99 wt. %KNO₃, based on the total weight of the ion exchange bath. In someembodiments, the ion exchange bath may include from 0 wt. % to 98 wt. %,from 0 wt. % to 80 wt. %, from 0 wt. % to 20 wt. %, from 20 wt. % to 99wt. %, from 20 wt. % to 98 wt. %, from 20 wt. % to 80 wt. %, from 80 wt.% to 99 wt. %, or from 80 wt. % to 98 wt. % KNO₃, based on the totalweight of the ion exchange bath. The ion exchange bath may optionallyinclude 0.1 wt. % to 2 wt. % silicic acid H₄SiO₄.

The ion exchange strengthening of the glass made from the glasscomposition may be conducted at an ion exchange temperature and for animmersion time sufficient to provide a target stress profile within theglass. For example, in embodiments, the ion exchange bath may bemaintained at a temperature of from 350° C. to 450° C. In otherembodiments, the ion exchange bath may be maintained at a temperature offrom 365° C. to 440° C. In some embodiments, the ion exchange may beconducted for an immersion time of from 0.1 hours to 36 hours. In otherembodiments, the ion exchange may be conducted for an immersion time offrom 0.1 hours to 30 hours, from 0.1 hours to 20 hours, from 0.1 hoursto 10 hours, from 1 hour to 36 hours, from 1 hour to 30 hours, from 1hour to 20 hours, from 1 hour to 10 hours, or from 10 hours to 20 hours.The immersion time of the ion exchange may depend on the thickness ofthe glass being ion exchanged. The immersion time of ion exchange mayalso depend on the glass composition as previously described in thisdisclosure. In some embodiments, for a flat glass sheet made from theglass composition and having a thickness of from 0.5 millimeters (mm) to1 mm, the ion exchange may be conducted for an immersion time of greaterthan or equal to 1 hour and less than or equal to 10 hours.

In some embodiments, the glass composition may enable the glass to beion exchanged until the sodium ions reach the center of the thickness ofthe glass. By ion exchanging the glass composition until the sodium ionsmeet in the center of the thickness of the glass, a sodium ionconcentration gradient through the thickness of the glass may begenerated, resulting in a parabolic stress profile through the thicknessof the glass. Referring to FIG. 1, the stress profiles of two exampleglasses made from the glass compositions are illustrated as a functionof the thickness through the glass. In FIG. 1, negative stress indicatescompressive stress and positive stress indicates tensile stress (i.e.,central tension (CT)). The DOC is the point at which the stress in theglass transitions from compressive stress (i.e., negative stress ofFIG. 1) to central tension (i.e., positive stress of FIG. 1). As shownin FIG. 1, the gradient of sodium ions penetrating into the centraltension region (i.e., the region from about 1.5 mm to about 6 mm inFIG. 1) makes the stress profile curved in the central tension region.Because the stress profile is curved in the central tension region, thetotal stored tension in the central tension region of the glass is less.If the central tension in the glass becomes too great, the glass maybecome frangible. Thus, by ion exchanging the glass to produce aparabolic stress profile that reduces the central tension in the glass,a greater DOC can be achieved without causing the glass to becomefrangible. As used herein, the terms “frangible behavior” and“frangibility” refer to those modes of violent or energeticfragmentation of the strengthened glass absent any external restraints,such as coatings, adhesive layers, or the like. While coatings, adhesivelayers, and the like may be used in conjunction with the strengthenedglass made from the glass compositions described herein, such externalrestraints are not used in determining the frangibility or frangiblebehavior of the glass.

In some embodiments, the parabolic stress profile may enable the centraltension in the glass composition to be less than 120 megaPascals (MPa),or even less than 100 MPa. In some embodiments, the central tension ofthe glass composition may be greater than or equal to 50 MPa and lessthan 120 MPa, or even greater than or equal to 70 MPa and less than orequal to 100 MPa. In some embodiments, 0.8 mm thick samples of the glassmade from the glass compositions disclosed herein are capable of beingion exchanged to a parabolic profile in less than 8 hours at 430° C.

In embodiments, after ion exchanging of the glass article or glass sheetmade from the glass composition to produce a parabolic stress profile,the DOC in the glass may be up to 15% of the thickness of the glass. Forexample, in some embodiments, after ion exchange of the glass to producea parabolic stress profile, the DOC may be up to 18% of the thickness ofthe glass, up to 20% of the thickness of the glass, up to 22% of thethickness of the glass, or even up to 25% of the thickness of the glass.In some embodiments, after ion exchange, the glass composition may havea DOC of from 5% to 25% of the thickness of the glass composition. Forexample, after ion exchange of the glass made from the glasscomposition, the glass may have a DOC of from 5% to 18%, from 5% to 20%,from 5% to 20%, from 5% to 22%, from 10% to 15%, from 10% to 18%, from10% to 20%, from 10% to 22%, from 10% to 25%, from 15% to 18%, from 15%to 20%, from 15% to 22%, from 15% to 25%, from 18% to 20%, or from 18%to 22% of the thickness of the glass. In one example, a sheet of theglass made from the glass compositions and having a thickness of 0.8 mmmay have a DOC of up to about 120 μm, or up to about 145 μm, or even upto about 160 μm. In another example, a sheet of glass made from theglass compositions and having a thickness of 1 mm may have a DOC of upto about 150 μm, or up to about 180 μm, or even up to about 200 μm. Ionexchanging the glass to attain a parabolic stress profile may enable theglass to have a DOC in a range of from 100 μm to 200 μm for glass havingthicknesses of from 0.5 mm to 1 mm. Typical conventional alkalialuminosilicate glasses have a DOC after ion exchange of from 40 μm to50 μm. Therefore, the glass compositions disclosed herein may enable ionexchange of glass made from the glass compositions to produce aparabolic stress profile in the glass, which may result in asubstantially greater DOC in the glass.

The glass compositions described herein enable the sodium ions tomigrate to the center of the glass during ion exchange. However,potassium ions, when present in the ion exchange bath, may not migrateas far into the glass made from the glass compositions compared to thesodium ions due to the larger size of the potassium ions compared to thesodium ions. In embodiments in which potassium ions are included in theion exchange bath, the potassium ions penetrate into the glass (K DOL)to a depth of from 5 μm to 25 μm, from 5 μm to 15 μm, or even from 8 μmto 12 μm.

In some embodiments, after ion exchange, the glass made from the glasscompositions may have a compressive stress sufficient to provide damageresistance to the glass. For example, in some embodiments, after ionexchange, the glass may have a compressive stress at the surface of theglass of greater than or equal to 400 MPa, greater than or equal to 500MPa, or even greater than or equal to 600 MPa.

In some embodiments, a second ion exchange step may be conducted tofurther increase the compressive stress in the outer regions of theglass formed from the glass compositions. Without being bound by theory,the second ion exchange step is considered to be a rapid ion exchangestep that yields a “spike” of compressive stress near the surface of theglass. In one or more embodiments, the second ion exchange step may beconducted for a time of 30 minutes or less, or for a time of 15 minutesor less, or optionally may be conducted in a range of about 10 to about15 minutes. The composition of the second ion exchange bath may bedifferent than the first ion exchange bath, such as when the second ionexchange step is directed to delivering a different ion to the glassthan the first ion exchange step. In some embodiments, the second ionexchange bath may comprise a potassium salt, such as potassium nitrate,potassium sulfate, potassium chloride, other potassium salt, orcombinations of these. In one or more embodiments, the second ionexchange bath may comprise at least about 80% by weight potassium salt.In a specific embodiment, the second ion exchange bath may comprise fromabout 95% to about 99.5% by weight potassium salt. While it is possiblethat the second ion exchange bath only comprises a potassium salt, thesecond ion exchange bath may, in some embodiments, comprise 0-2% byweight, or about 0.5-1.5% by weight sodium salt, for example, NaNO₃. Inan exemplary embodiment, the potassium salt is KNO₃. In furtherembodiments, the temperature of the second ion exchange step may be 390°C. or greater. If the compressive stress in the ion exchanged glassfollowing the first ion exchange is not sufficient, then the second ionexchange step may be conducted to “spike” the outer surface of the glasswith potassium ions to increase the compressive stress at the surface ofthe glass.

The glasses made from the glass compositions described herein maygenerally have a strain point greater than or equal to about 500° C. andless than or equal to about 650° C. The glasses made from the glasscompositions disclosed herein may also have an anneal point greater thanor equal to about 550° C. and less than or equal to about 725° C. and asoftening point greater than or equal to about 775° C. and less than orequal to about 960° C.

In the embodiments described herein the glass made from the glasscomposition may have a CTE of less than about 75×10⁻⁷ K⁻¹ or even lessthan about 60×10⁻⁷ K⁻¹. These lower CTE values improve the survivabilityof the glass to thermal cycling or thermal stress conditions relative toglass compositions with higher CTEs.

The glass articles disclosed herein may be incorporated into anotherarticle such as an article with a display (or display articles) (e.g.,consumer electronics, including mobile phones, tablets, computers,navigation systems, and the like), architectural articles,transportation articles (e.g., automotive, trains, aircraft, sea craft,etc.), appliance articles, or any article that requires sometransparency, scratch-resistance, abrasion resistance or a combinationthereof. An exemplary article incorporating any of the glass articlesdisclosed herein is shown in FIGS. 2A and 2B. Specifically, FIGS. 2A and2B show a consumer electronic device 300 including a housing 302 havingfront 304, back 306, and side surfaces 308; electrical components (notshown) that are at least partially inside or entirely within the housingand including at least a controller, a memory, and a display 310 at oradjacent to the front surface of the housing; and a cover substrate 312at or over the front surface of the housing such that it is over thedisplay. In some embodiments, at least one of the cover substrate 312 ora portion of housing 302 may include any of the glass articles disclosedherein.

EXAMPLES

The embodiments of the glass compositions described herein will befurther clarified by the following examples.

Example 1

103 exemplary glass compositions (compositions 1-103) were prepared. Thespecific compositions of each exemplary glass composition are reportedbelow in Table 1. The constituents of the glass compositions were meltedin platinum crucibles between 1500° C. and 1600° C. for 5 to 6 hours,and then re-melted at a higher temperature between 1600° C. and 1650° C.for 5 to 6 hours to improve homogeneity and melt quality. The liquidustemperature and liquidus viscosity of the glass compositions of Example1 were measured. The glasses were then cast onto a steel plate andannealed for 1 hour near the anneal temperatures given in Table I.Multiple samples of each glass composition were cut and polished forproperty measurements and further ion exchange experiments. All of thesamples were 0.8 mm in thickness. Each of the samples were tested forcoefficient of thermal expansion (CTE), density, toughness, and Young'smodulus. The density values recited in this disclosure refer to a valueas measured by the buoyancy method of ASTM C693-93(2013). The Young'smodulus values recited in this disclosure refer to a value as measuredby a resonant ultrasonic spectroscopy technique of the general type setforth in ASTM E2001-13, titled “Standard Guide for Resonant UltrasoundSpectroscopy for Defect Detection in Both Metallic and Non-metallicParts.” In some embodiments, the Young's modulus is greater than orequal to 70 GPa or greater than or equal to 80 GPa. The results for allof the glass compositions are reported below in Table 1. The fracturetoughness value (Kw) recited in this disclosure refers to a value asmeasured by chevron notched short bar (CNSB) method disclosed in Reddy,K. P. R. et al, “Fracture Toughness Measurement of Glass and CeramicMaterials Using Chevron-Notched Specimens,” J. Am. Ceram. Soc., 71 [6],C-310-C-313 (1988) except that Y*_(m) is calculated using equation 5 ofBubsey, R. T. et al., “Closed-Form Expressions for Crack-MouthDisplacement and Stress Intensity Factors for Chevron-Notched Short Barand Short Rod Specimens Based on Experimental Compliance Measurements,”NASA Technical Memorandum 83796, pp. 1-30 (October 1992). In someembodiments, the fracture toughness is greater than or equal to about0.7 MPa·m^(1/2) or greater than or equal to about 0.7 MPa·m^(1/2).

TABLE 1 Glass Compositions and Properties of Example 1 Composition Mole% Composition ID 1 2 3 4 5 6 7 SiO₂ 65.042 73.659 65.212 67.242 63.51763.433 61.511 Al₂O₃ 13.457 12.874 13.933 11.921 14.877 14.848 15.853B₂O₃ 6.666 0.000 7.738 5.736 7.630 7.610 7.545 P₂O₅ 5.231 — 3.956 5.9113.956 3.976 3.983 Li₂O 8.065 6.012 7.982 8.018 7.817 8.831 9.794 Na₂O0.823 1.926 0.962 0.960 1.061 1.062 1.059 K₂O 0.044 0.034 0.041 0.0420.029 0.032 0.037 MgO 0.032 2.001 0.024 0.020 0.934 0.027 0.027 CaO0.533 1.960 0.045 0.043 0.055 0.052 0.058 ZnO 0.000 0.000 0.000 0.0000.000 0.000 0.000 SnO₂ 0.079 0.075 0.079 0.079 0.082 0.083 0.082 ZrO₂0.000 0.000 0.000 0.000 0.001 0.001 0.001 TiO₂ 0.002 0.008 0.002 0.0020.002 0.002 0.003 HfO₂ 0.000 0.000 0.000 0.000 0.006 0.006 0.006 Fe₂O₃0.019 0.017 0.020 0.020 0.020 0.022 0.024 MnO₂ 0.000 — — — 0.008 0.0090.010 SrO 0.000 — — — — — — R₂O—Al₂O₃ −4.525 −4.903 −4.948 −2.900 −5.970−4.922 −4.963 R₂O+RO—Al₂O₃ −3.960 −0.942 −4.880 −2.837 −4.981 −4.843−4.877 R₂O+RO+P₂O₅— 1.271 −0.942 −0.923 3.073 −1.024 −0.867 −0.894 Al₂O₃Li₂O/R₂O 0.903 0.754 0.888 0.889 0.878 0.890 0.899 Strain (° C.) 535 657539 518 545 539 539 Anneal (° C.) 589 708 593 573 597 592 590 Softening(° C.) 872 953 870 874 860.3 854.1 839.5 CTE (10⁻⁷ ° C.⁻¹) 44.2 46.143.3 45.2 41.6 44.6 47.2 Density (g/cm³) 2.284 2.512 2.29 2.273 2.3072.302 2.313 Liq. T (° C.) 1230 1235 1175 1250 1185 1140 1165 Liq. Vise.(kP) 22.3 42.2 50.3 29.4 24.6 51.3 21.9 Fracture 0.674 0.808 0.718 0.708— 0.723 0.758 Toughness (MPa · m^(1/2)) Young's Mod. 78.94 84.67 68.8167.09 70.46 69.64 70.46 (GPa) Composition Mole % Composition ID 8 9 1011 12 13 14 SiO₂ 65.372 62.398 58.517 67.097 67.176 67.120 68.099 Al₂O₃14.863 17.822 17.789 13.983 13.987 13.977 12.993 B₂O₃ 6.299 0.000 0.0005.856 5.853 5.824 5.844 P₂O₅ 3.321 1.975 5.850 2.922 2.932 2.937 2.935Li₂O 8.837 11.678 11.696 8.910 7.851 6.953 7.911 Na₂O 1.061 5.820 5.8340.971 1.955 2.954 1.970 K₂O 0.034 0.041 0.042 0.044 0.039 0.035 0.038MgO 0.030 0.036 0.038 0.020 0.020 0.015 0.020 CaO 0.055 0.070 0.0730.049 0.045 0.042 0.045 ZnO 0.000 0.000 0.000 0.002 0.002 0.002 0.001SnO₂ 0.082 0.104 0.103 0.083 0.080 0.083 0.083 ZrO₂ 0.001 0.001 0.0010.010 0.009 0.010 0.010 TiO₂ 0.003 0.003 0.003 0.006 0.008 0.010 0.008HfO₂ 0.006 0.000 0.000 0.000 0.000 0.000 0.000 Fe₂O₃ 0.023 0.029 0.0290.023 0.021 0.019 0.020 MnO₂ 0.009 0.014 0.015 0.018 0.015 0.011 0.015SrO — — — — — — — R₂O—Al₂O₃ −4.931 −0.284 −0.217 −4.058 −4.142 −4.035−3.074 R₂O+RO—Al₂O₃ −4.846 −0.178 −0.107 −3.988 −4.075 −3.976 −3.008R₂O+RO+P₂O₅— −1.525 1.796 5.744 −1.066 −1.143 −1.039 −0.073 Al₂O₃Li₂O/R₂O 0.890 0.666 0.666 0.898 0.797 0.699 0.798 Strain (° C.) 557 613566 573 563 564 557 Anneal (° C.) 610 662 615 627 620 620 613 Softening(° C.) 877.8 xtl 857.2 889.5 891.1 893.3 877.9 CTE (10⁻⁷ ° C.⁻¹) 44.2 7475.3 44.9 46.1 47.8 47.3 Density (g/cm³) 2.313 2.41 2.395 2.309 2.3112.313 2.303 Liq. T (° C.) 1195 1170 1160 1135 1105 1075 1165 Liq. Vise.(kP) 27.4 35.9 26.6 120.2 240.5 455.7 92.5 Fracture 0.745 0.74 0.7160.776 0.768 0.709 0.688 Toughness (MPa · m^(1/2)) Young's Mod. 71.5780.88 76.67 72.12 72.12 71.29 70.12 (GPa) Composition Mole % CompositionID 15 16 17 18 19 20 21 SiO₂ 67.135 67.134 67.972 68.095 67.855 68.17367.126 Al₂O₃ 13.987 13.956 14.968 15.010 14.939 15.031 14.002 B₂O₃ 6.7964.878 3.924 2.694 1.856 2.724 4.877 P₂O₅ 1.957 3.886 1.955 2.931 3.8931.963 3.959 Li₂O 7.895 7.923 8.008 8.077 8.288 7.950 7.393 Na₂O 1.9711.974 2.926 2.943 2.918 3.912 2.421 K₂O 0.039 0.039 0.037 0.037 0.0370.039 0.037 MgO 0.018 0.018 0.021 0.020 0.022 0.025 0.024 CaO 0.0450.046 0.046 0.047 0.046 0.045 0.044 ZnO 0.001 0.002 0.001 0.002 0.0020.002 0.000 SnO₂ 0.083 0.083 0.083 0.084 0.084 0.083 0.073 ZrO₂ 0.0060.009 0.005 0.007 0.009 0.004 0.001 TiO₂ 0.009 0.007 0.007 0.008 0.0070.004 0.010 HfO₂ 0.000 0.000 0.000 0.000 0.000 0.000 0.000 Fe₂O₃ 0.0200.021 0.021 0.021 0.021 0.021 0.020 MnO₂ 0.014 0.015 0.015 0.015 0.0130.015 0.008 SrO — — — — — — — R₂O—Al₂O₃ −4.082 −4.018 −3.997 −3.953−3.695 −3.131 −4.151 R₂O+RO—Al₂O₃ −4.018 −3.952 −3.928 −3.885 −3.626−3.059 −4.084 R₂O+RO+P₂O₅— −2.061 −0.066 −1.973 −0.954 0.268 −1.096−0.125 Al₂O₃ Li₂O/R₂O 0.797 0.797 0.730 0.730 0.737 0.668 0.750 Strain(° C.) 561 564 598 604 610 598 565 Anneal (° C.) 616 620 654 660 667 654621 Softening (° C.) — 900.7 920.9 935.9 950.7 925.1 905.9 CTE (10⁻⁷ °C.⁻¹) 45.5 47 49.7 49.9 50.7 54.8 48.2 Density (g/cm³) 2.315 2.308 2.3422.338 2.335 2.351 2.309 Liq. T (° C.) 1210 1095 1250 1175 1180 1170 1090Liq. Visc. (kP) 28.0 407.3 25.9 123.6 162.7 116.1 478.4 Fracture 0.7620.715 0.759 0.739 0.735 0.759 0.734 Toughness (MPa · m^(1/2)) Young'sMod. 72.12 70.95 74.95 74.88 74.46 76.26 70.67 (GPa) Composition Mole %Composition ID 22 23 24 25 26 27 28 SiO₂ 67.105 65.781 66.097 65.23767.097 67.176 65.050 Al₂O₃ 13.976 13.717 14.974 13.586 13.971 14.00613.353 B₂O₃ 4.920 4.802 3.903 4.743 4.890 5.815 6.893 P₂O₅ 3.957 3.8734.943 3.850 3.966 2.978 3.195 Li₂O 6.923 6.821 6.947 7.590 7.919 7.8708.847 Na₂O 2.905 2.849 2.913 1.879 1.931 1.932 2.421 K₂O 0.035 0.0340.034 0.038 0.040 0.040 0.044 MgO 0.024 1.959 0.026 2.899 0.025 0.0220.018 CaO 0.041 0.053 0.044 0.061 0.046 0.044 0.049 ZnO 0.000 0.0000.000 0.000 0.000 0.000 0.002 SnO₂ 0.073 0.071 0.074 0.071 0.073 0.0730.062 ZrO₂ 0.001 0.001 0.001 0.001 0.001 0.001 0.008 TiO₂ 0.008 0.0080.011 0.008 0.006 0.008 0.007 HfO₂ 0.000 0.000 0.000 0.000 0.000 0.0000.000 Fe₂O₃ 0.019 0.019 0.019 0.022 0.021 0.021 0.023 MnO₂ 0.008 0.0060.006 0.009 0.008 0.008 0.020 SrO — — — — — — — R₂O—Al₂O₃ −4.113 −4.013−5.080 −4.079 −4.081 −4.165 −2.041 R₂O+RO—Al₂O₃ −4.048 −2.001 −5.010−1.119 −4.010 −4.099 −1.972 R₂O+RO+P₂O₅— −0.091 1.872 −0.067 2.731−0.044 −1.121 1.223 Al₂O₃ Li₂O/R₂O 0.702 0.703 0.702 0.798 0.801 0.8000.782 Strain (° C.) 559 555 576 558 566 559 525 Anneal (° C.) 617 608634 609 623 614 578 Softening (° C.) 904.5 875.3 921.2 — — — 839.8 CTE(10⁻⁷ ° C.⁻¹) 48.8 49 48.8 47.3 47 47.1 53.2 Density (g/cm³) 2.31 2.3292.315 2.335 2.308 2.311 2.309 Liq. T (° C.) 1105 1070 1175 1100 11001135 1085 Liq. Visc. (kP) 367.9 410.1 123.8 153.2 384.4 139.5 132.3Fracture 0.725 0.749 0.724 — — — 0.771 Toughness (MPa · m^(1/2)) Young'sMod. 70.67 72.33 70.95 73.22 70.88 71.29 69.84 (GPa) Composition Mole %Composition ID 29 30 31 32 33 34 35 SiO₂ 65.803 66.519 65.457 66.02166.364 65.862 66.642 Al₂O₃ 13.515 13.654 13.017 13.153 13.233 13.01713.216 B₂O₃ 6.957 6.882 6.964 7.075 7.073 7.030 6.936 P₂O₅ 3.241 3.2623.235 3.267 3.292 3.241 3.271 Li₂O 7.812 7.011 8.302 7.448 6.995 7.8106.891 Na₂O 2.440 2.453 2.329 2.354 2.361 2.343 2.361 K₂O 0.041 0.0360.045 0.038 0.036 0.045 0.039 MgO 0.017 0.018 0.492 0.491 0.494 0.4960.493 CaO 0.046 0.043 0.051 0.045 0.051 0.051 0.045 ZnO 0.001 0.0020.000 0.000 0.000 0.000 0.001 SnO₂ 0.062 0.064 0.062 0.064 0.063 0.0620.063 ZrO₂ 0.008 0.008 0.001 0.001 0.001 0.001 0.001 TiO₂ 0.006 0.0070.007 0.008 0.007 0.008 0.008 HfO₂ 0.000 0.000 0.000 0.000 0.000 0.0000.000 Fe₂O₃ 0.021 0.019 0.022 0.019 0.019 0.020 0.019 MnO₂ 0.017 0.0140.010 0.008 0.007 0.008 0.008 SrO — — — — — — — R₂O—Al₂O₃ −3.222 −4.154−2.341 −3.312 −3.842 −2.820 −3.925 R₂O+RO—Al₂O₃ −3.159 −4.090 −1.798−2.776 −3.297 −2.272 −3.386 R₂O+RO+P₂O₅— 0.082 −0.828 1.437 0.491 −0.0050.969 −0.115 Al₂O₃ Li₂O/R₂O 0.759 0.738 0.778 0.757 0.745 0.766 0.742Strain (° C.) 534 543 520 534 547 531 545 Anneal (° C.) 588 599 573 588601 584 600 Softening (° C.) 864.2 883.3 839.4 866.3 877.2 856.1 877.3CTE (10⁻⁷ ° C.⁻¹) 50.3 46.9 52 48.4 47.4 50 46.9 Density (g/cm³) 2.3042.301 2.308 2.303 2.301 2.304 2.301 Liq. T (° C.) 1060 1060 1070 10551045 1060 1035 Liq. Visc. (kP) 343.9 500.9 206.1 402.9 627.4 275.5 759.5Fracture 0.721 0.704 0.749 0.731 0.709 0.709 0.719 Toughness (MPa ·m^(1/2)) Young's Mod. 69.50 69.77 69.91 69.57 69.57 69.50 69.43 (GPa)Composition Mole % Composition ID 36 37 38 39 40 41 42 SiO₂ 67.37870.725 63.113 63.643 63.075 63.756 64.583 Al₂O₃ 13.373 12.641 13.94314.048 13.352 13.470 13.645 B₂O₃ 6.857 3.866 7.013 7.362 7.216 7.3367.258 P₂O₅ 3.311 0.029 3.214 3.244 3.179 3.198 3.249 Li₂O 6.025 6.6329.889 8.878 9.871 8.924 7.919 Na₂O 2.385 2.441 2.607 2.618 2.539 2.5582.587 K₂O 0.034 0.034 0.046 0.041 0.045 0.042 0.037 MgO 0.494 2.7360.026 0.023 0.568 0.568 0.580 CaO 0.042 0.055 0.049 0.045 0.053 0.0480.044 ZnO 0.000 0.690 0.000 0.000 0.000 0.000 0.002 SnO₂ 0.064 0.1020.053 0.052 0.054 0.053 0.054 ZrO₂ 0.001 0.000 0.001 0.001 0.001 0.0010.001 TiO₂ 0.009 0.008 0.006 0.006 0.006 0.007 0.007 HfO₂ 0.000 0.0000.000 0.000 0.000 0.000 0.000 Fe₂O₃ 0.017 0.019 0.025 0.022 0.025 0.0220.020 MnO₂ 0.005 0.013 0.011 0.010 0.011 0.010 0.007 SrO — — — — — — —R₂O—Al₂O₃ −4.930 −3.534 −1.402 −2.512 −0.897 −1.947 −3.102 R₂O+RO—Al₂O₃−4.395 −0.053 −1.327 −2.443 −0.276 −1.331 −2.475 R₂O+RO+P₂O₅— −1.084−0.024 1.887 0.801 2.903 1.867 0.774 Al₂O₃ Li₂O/R₂O 0.714 0.728 0.7880.770 0.793 0.774 0.751 Strain (° C.) 553 590 510 521 506 520 530 Anneal(° C.) 609 643 560 574 556 571 583 Softening (° C.) 898.9 909.5 809.7834 799.4 822.9 849.7 CTE (10⁻⁷ ° C.⁻¹) 43.4 45.2 55.1 52.8 56.2 52.849.9 Density (g/cm³) 2.299 2.371 2.316 2.311 2.32 2.313 2.309 Liq. T (°C.) 1005 1175 1090 1075 1075 1065 1060 Liq. Vise. (kP) 2250.7 66.2 76.3134.0 70.9 159.9 304.1 Fracture 0.702 0.799 0.766 0.7 0.692 0.718 0.704Toughness (MPa · m^(1/2)) Young's Mod. 69.50 79.01 69.77 69.64 70.5370.05 69.84 (GPa) Composition Mole % Composition ID 43 44 45 46 47 48 49SiO₂ 65.216 65.163 65.169 65.217 65.135 65.247 70.846 Al₂O₃ 13.58513.599 13.593 13.609 13.592 13.559 12.592 B₂O₃ 4.707 4.687 4.658 4.6644.728 4.691 4.108 P₂O₅ 3.837 3.821 3.836 3.847 3.854 3.855 0.003 Li₂O7.705 7.758 7.761 7.714 7.711 7.664 6.466 Na₂O 1.876 1.907 1.945 1.8741.878 1.876 2.417 K₂O 0.040 0.038 0.039 0.039 0.039 0.040 0.003 MgO1.937 1.942 0.982 0.971 1.933 0.975 2.773 CaO 0.997 0.054 0.048 1.9630.067 0.076 0.718 ZnO 0.000 0.936 1.872 0.000 0.000 0.000 0.000 SnO₂0.052 0.052 0.052 0.052 0.051 0.049 0.052 ZrO₂ 0.001 0.001 0.001 0.0010.001 0.000 0.001 TiO₂ 0.007 0.008 0.007 0.008 0.007 0.007 0.008 HfO₂0.000 0.000 0.000 0.000 0.000 0.000 0.000 Fe₂O₃ 0.022 0.021 0.021 0.0230.021 0.022 0.005 MnO₂ 0.010 0.007 0.007 0.008 0.008 0.008 0.000 SrO0.001 0.000 0.000 0.002 0.969 1.926 0.001 R₂O—Al₂O₃ −3.964 −3.896 −3.848−3.983 −3.963 −3.978 −3.705 R₂O+RO—Al₂O₃ −1.030 −0.964 −0.946 −1.048−1.963 −2.927 −0.214 R₂O+RO+P₂O₅— 2.807 2.857 2.889 2.799 1.891 0.928−0.211 Al₂O₃ Li₂O/R₂O 0.801 0.800 0.796 0.801 0.801 0.800 0.728 Strain(° C.) 549 542 553 553 545 546 559 Anneal (° C.) 600 593 604 604 597 598612 Softening (° C.) 858.9 853.7 862.4 857 858.3 861 875.4 CTE (10⁻⁷ °C.⁻¹) 46.9 46.8 50.3 49.5 49 50.5 53.3 Density (g/cm³) 2.347 2.358 2.3392.343 2.352 2.37 2.331 Liq. T (° C.) 1115 1120 1120 1110 1105 1100 1140Liq. Vise. (kP) 104.7 93.2 101.6 120.0 132.5 146.2 94.6 Fracture — — — —— — 0.722 Toughness (MPa · m^(1/2)) Young's Mod. 73.50 72.81 73.50 72.9573.02 72.88 72.95 (GPa) Composition Mole % Composition ID 50 51 52 53 5455 56 SiO₂ 70.699 70.828 70.725 70.751 72.113 70.846 70.699 Al₂O₃ 13.08013.608 13.561 13.580 12.914 12.592 13.080 B₂O₃ 4.220 4.035 4.230 4.1684.061 4.108 4.220 P₂O₅ 0.004 0.004 0.004 0.004 0.004 0.003 0.004 Li₂O6.470 6.489 6.491 6.495 6.151 6.466 6.470 Na₂O 2.419 2.424 2.416 3.4092.299 2.417 2.419 K₂O 0.003 0.003 0.003 0.003 0.003 0.003 0.003 MgO2.307 1.799 0.796 0.791 0.763 2.773 2.307 CaO 0.725 0.734 1.701 0.7241.618 0.718 0.725 ZnO 0.000 0.000 0.000 0.000 0.000 0.000 0.000 SnO₂0.052 0.054 0.053 0.052 0.050 0.052 0.052 ZrO₂ 0.001 0.002 0.001 0.0010.002 0.001 0.001 TiO₂ 0.008 0.008 0.007 0.008 0.009 0.008 0.008 HfO₂0.000 0.000 0.000 0.000 0.000 0.000 0.000 Fe₂O₃ 0.005 0.005 0.005 0.0040.005 0.005 0.005 MnO₂ 0.000 0.000 0.000 0.000 0.000 0.000 0.000 SrO0.001 0.001 0.001 0.001 0.001 0.001 0.001 R₂O—Al₂O₃ −4.188 −4.692 −4.650−3.673 −4.460 −3.705 −4.188 R₂O+RO—Al₂O₃ −1.156 −2.159 −2.154 −2.157−2.079 −0.214 −1.156 R₂O+RO+P₂O₅— −1.153 −2.156 −2.150 −2.153 −2.075−0.211 −1.153 Al₂O₃ Li₂O/R₂O 0.728 0.728 0.728 0.656 0.728 0.728 0.728Strain (° C.) 552 572 582 554 583 598 601 Anneal (° C.) 605 625 632 609635 650 654 Softening (° C.) 863.6 879.8 872.5 877.2 884.6 915 917 CTE(10⁻⁷ ° C.⁻¹) 59.7 48.2 50.4 60.9 50.6 46 45 Density (g/cm³) 2.349 2.3412.37 2.347 2.367 2.36 2.361 Liq. T (° C.) 1145 1140 1160 1145 1165 11801210 Liq. Visc. (kP) 62.1 82.9 37.5 90.6 46.6 63.2 45.9 Fracture 0.7410.742 0.73 0.733 0.73 0.766 0.758 Toughness (MPa · m^(1/2)) Young's Mod.74.05 73.91 77.29 73.70 76.81 78.53 79.15 (GPa) Composition Mole %Composition ID 57 58 59 60 61 62 63 SiO₂ 68.275 66.556 67.259 67.29465.469 66.423 67.059 Al₂O₃ 13.943 14.777 14.426 14.936 14.687 14.37414.115 B₂O₃ 4.976 4.924 3.979 2.992 3.222 4.192 5.106 P₂O₅ 2.942 3.8763.924 3.920 2.755 2.836 2.910 Li₂O 7.789 7.815 7.821 7.766 7.295 7.4377.616 Na₂O 1.952 1.929 1.964 1.951 5.866 4.232 2.864 K₂O 0.003 0.0030.003 0.004 0.032 0.033 0.033 MgO 0.015 0.017 0.027 0.037 0.017 0.0180.017 CaO 0.020 0.019 0.505 1.010 0.035 0.036 0.037 ZnO 0.001 0.0010.001 0.001 0.507 0.294 0.116 SnO₂ 0.052 0.051 0.052 0.051 0.077 0.0870.084 ZrO₂ 0.008 0.010 0.010 0.010 0.014 0.012 0.014 TiO₂ 0.010 0.0090.009 0.010 0.000 0.000 0.000 HfO₂ 0.000 0.000 0.000 0.000 — — — Fe₂O₃0.005 0.005 0.005 0.006 0.018 0.019 0.019 MnO₂ 0.003 0.000 0.000 0.0020.006 0.008 0.010 SrO — — — — — — — R₂O—Al₂O₃ −4.200 −5.031 −4.639−5.216 −1.495 −2.672 −3.602 R₂O+RO—Al₂O₃ −4.164 −4.994 −4.106 −4.167−0.937 −2.324 −3.433 R₂O+RO+P₂O₅— Al₂O₃ −1.222 −1.118 −0.182 −0.2471.818 0.512 −0.523 Li₂O/R₂O 0.799 0.802 0.799 0.799 0.553 0.636 0.724Strain (° C.) 577 582 573 585 550 548 553 Anneal (° C.) 633 639 630 641604 603 608 Softening (° C.) 916 915.3 916.2 931.6 — 892.6 — CTE (10⁻⁷ °C.⁻¹) 46.1 45.8 46.9 47 — 53.8 — Density (g/cm³) 2.312 2.311 2.319 2.334— 2.336 — Liq. T (° C.) 1160 1195 1140 1180 1095 1105 1105 Liq. Visc.(kP) 129.0 58.3 199.1 105.5 237.9 193.0 213.9 Fracture 0.722 0.712 0.7320.712 — — — Toughness (MPa · m^(1/2)) Young's Mod. 72.05 71.64 72.3374.33 73.22 72.60 71.91 (GPa) Composition Mole % Composition ID 64 65 6667 68 69 70 SiO₂ 67.580 67.720 67.076 66.660 66.588 66.233 66.389 Al₂O₃13.908 13.907 13.767 13.660 13.609 13.653 13.628 B₂O₃ 5.603 5.436 5.5315.394 5.287 5.417 5.321 P₂O₅ 2.953 2.944 3.156 3.318 3.373 3.364 3.365Li₂O 7.810 7.840 7.753 7.743 7.744 7.796 7.773 Na₂O 1.937 1.917 1.9061.894 1.908 1.912 1.916 K₂O 0.032 0.033 0.032 0.032 0.032 0.011 0.003MgO 0.018 0.020 0.624 1.133 1.284 1.473 1.478 CaO 0.036 0.038 0.0420.045 0.046 0.030 0.023 ZnO 0.002 0.000 0.000 0.000 0.000 0.000 0.000SnO₂ 0.081 0.099 0.075 0.080 0.087 0.090 0.087 ZrO₂ 0.012 0.018 0.0100.011 0.014 0.013 0.014 TiO₂ 0.000 0.000 0.000 0.000 0.000 0.000 0.000HfO₂ — — — — — — — Fe₂O₃ 0.019 0.020 0.019 0.020 0.020 0.009 0.005 MnO₂0.008 0.010 0.008 0.010 0.009 0.000 0.000 SrO — — — — — — — R₂O—Al₂O₃−4.129 −4.118 −4.077 −3.991 −3.926 −3.933 −3.937 R₂O+RO—Al₂O₃ −4.073−4.060 −3.410 −2.813 −2.596 −2.431 −2.436 R₂O+RO+P₂O₅— −1.120 −1.116−0.255 0.506 0.777 0.933 0.929 Al₂O₃ Li₂O/R₂O 0.799 0.801 0.800 0.8010.800 0.802 0.802 Strain (° C.) 556 562 552 548 548 555 554 Anneal (°C.) 611 618 606 602 602 608 608 Softening (° C.) — — — — 885.8 — — CTE(10⁻⁷ ° C.⁻¹) — — — — 44.9 — — Density (g/cm³) 2.306 2.307 2.309 — 2.314— — Liq. T (° C.) 1140 1160 1075 1095 1080 1095 1095 Liq. Visc. (kP)130.7 99.3 380.6 241.5 320.2 226.6 227.0 Fracture — — — — — — —Toughness (MPa · m^(1/2)) Young's Mod. 71.36 72.12 71.50 72.74 72.0571.91 72.46 (GPa) Composition Mole % Composition ID 71 72 73 74 75 76 77SiO₂ 66.295 65.647 65.470 65.706 66.240 66.626 67.088 Al₂O₃ 13.37513.363 13.402 13.724 13.786 13.811 14.051 B₂O₃ 5.288 4.975 4.868 4.8174.930 4.985 5.007 P₂O₅ 3.462 3.710 3.826 3.818 3.826 3.847 3.876 Li₂O7.754 7.710 7.509 7.738 7.672 7.731 7.905 Na₂O 1.920 1.895 1.891 1.9101.945 1.953 1.978 K₂O 0.003 0.003 0.003 0.003 0.003 0.003 0.002 MgO1.782 2.570 2.937 2.197 1.520 0.967 0.028 CaO 0.024 0.028 0.028 0.0260.022 0.018 0.014 ZnO 0.000 0.000 0.000 0.000 0.000 0.000 0.000 SnO₂0.084 0.084 0.044 0.042 0.037 0.038 0.035 ZrO₂ 0.009 0.010 0.015 0.0140.015 0.016 0.010 TiO₂ 0.000 0.000 0.000 0.000 0.000 0.000 0.000 HfO₂ —— — — — — — Fe₂O₃ 0.004 0.005 0.005 0.005 0.005 0.004 0.004 MnO₂ 0.0000.000 0.000 0.000 0.000 0.000 0.000 SrO — — — — — — — R₂O—Al₂O₃ −3.698−3.756 −3.999 −4.073 −4.166 −4.124 −4.166 R₂O+RO—Al₂O₃ −1.892 −1.157−1.033 −1.850 −2.625 −3.140 −4.123 R₂O+RO+P₂O₅— Al₂O₃ 1.570 2.553 2.7931.968 1.201 0.707 −0.247 Li₂O/R₂O 0.801 0.803 0.799 0.802 0.798 0.7980.800 Strain (° C.) 552 553 554 554 557 560 561 Anneal (° C.) 606 605605 607 611 615 618 Softening (° C.) — — 878.9 — — — — CTE (10⁻⁷ ° C.⁻¹)— — 44.5 — — — — Density (g/cm³) — — 2.323 2.319 2.312 — 2.299 Liq. T (°C.) 1080 1105 1110 1095 1105 1085 1100 Liq. Visc. (kP) 287.5 159.0 132.3212.7 218.4 386.7 371.4 Fracture — — — — — — — Toughness (MPa · m^(1/2))Young's Mod. 72.74 73.02 73.36 73.02 73.43 72.05 71.15 (GPa) CompositionMole % Composition ID 78 79 80 81 82 83 84 SiO₂ 67.141 67.052 67.87968.890 69.710 70.794 70.029 Al₂O₃ 14.181 14.128 13.897 13.534 13.24112.979 13.370 B₂O₃ 5.134 5.085 4.646 4.431 4.336 4.060 3.953 P₂O₅ 3.9773.987 3.068 2.022 1.268 0.011 0.474 Li₂O 8.236 8.587 8.290 7.652 7.0156.202 6.690 Na₂O 1.236 1.062 1.255 1.556 1.786 2.156 2.588 K₂O 0.0030.002 0.003 0.003 0.003 0.004 0.003 MgO 0.018 0.023 0.467 0.960 1.3251.930 1.462 CaO 0.013 0.013 0.428 0.897 1.251 1.808 1.382 ZnO 0.0000.000 0.000 0.000 0.000 0.000 0.000 SnO₂ 0.045 0.046 0.049 0.040 0.0400.045 0.039 ZrO₂ 0.011 0.011 0.015 0.010 0.021 0.006 0.005 TiO₂ 0.0000.000 0.000 0.000 0.000 0.000 0.000 HfO₂ — — — — — — — Fe₂O₃ 0.004 0.0040.004 0.005 0.005 0.006 0.005 MnO₂ 0.000 0.000 0.000 0.000 0.000 0.0000.000 SrO — — — — — — — R₂O—Al₂O₃ −4.705 −4.477 −4.349 −4.323 −4.436−4.617 −4.089 R₂O+RO—Al₂O₃ −4.674 −4.440 −3.454 −2.465 −1.860 −0.880−1.245 R₂O+RO+P₂O₅— Al₂O₃ −0.697 −0.453 −0.386 −0.443 −0.593 −0.868−0.771 Li₂O/R₂O 0.869 0.890 0.868 0.831 0.797 0.742 0.721 Strain (° C.)565 564 571 581 585 601 595 Anneal (° C.) 620 619 626 636 639 654 649Softening (° C.) — 907.4 — — — — — CTE (10⁻⁷ ° C.⁻¹) — 43.6 — — — — —Density (g/cm³) — 2.297 — — — 2.359 — Liq. T (° C.) 1120 1125 1140 11401170 1160 1170 Liq. Vise. (kP) 206.3 190.3 132.4 139.6 80.3 101.0 86.3Fracture — — — — — — — Toughness (MPa · m^(1/2)) Young's Mod. 71.0870.74 73.02 74.88 76.46 78.88 78.19 (GPa) Composition Mole % CompositionID 85 86 87 88 89 90 91 SiO₂ 69.183 67.958 67.657 67.562 67.122 66.92966.957 Al₂O₃ 14.117 15.142 14.961 14.522 14.255 14.107 14.019 B₂O₃ 3.6023.011 3.567 4.337 5.309 5.635 5.545 P₂O₅ 1.079 1.951 2.285 2.739 3.3173.454 3.382 Li₂O 7.106 7.856 7.812 7.924 8.071 8.223 8.393 Na₂O 3.1293.900 3.604 2.814 1.829 1.543 1.609 K₂O 0.003 0.003 0.003 0.003 0.0030.003 0.003 MgO 0.894 0.062 0.026 0.023 0.020 0.020 0.015 CaO 0.8370.061 0.024 0.019 0.017 0.017 0.016 ZnO 0.000 0.000 0.000 0.000 0.0000.000 0.000 SnO₂ 0.039 0.043 0.048 0.046 0.044 0.050 0.045 ZrO₂ 0.0060.009 0.008 0.008 0.010 0.016 0.013 TiO₂ 0.000 0.000 0.000 0.000 0.0000.000 0.000 HfO₂ — — — — — — — Fe₂O₃ 0.005 0.004 0.004 0.004 0.004 0.0040.005 MnO₂ 0.000 0.000 0.000 0.000 0.000 0.000 0.000 SrO — — — — — — —R₂O—Al₂O₃ −3.880 −3.383 −3.543 −3.781 −4.352 −4.339 −4.014 R₂O+RO—Al₂O₃−2.148 −3.259 −3.493 −3.739 −4.316 −4.302 −3.984 R₂O+RO+P₂O₅— −1.069−1.308 −1.207 −1.000 −0.999 −0.849 −0.602 Al₂O₃ Li₂O/R₂O 0.694 0.6680.684 0.738 0.815 0.842 0.839 Strain (° C.) 593 595 584 573 563 560 556Anneal (° C.) 648 651 640 629 619 615 612 Softening (° C.) — — — — — — —CTE (10⁻⁷ ° C.⁻¹) — — — — — — — Density (g/cm³) 2.351 2.344 — — — 2.32.3 Liq. T (° C.) 1185 1180 1185 1160 1155 1140 1155 Liq. Vise. (kP)71.1 91.3 76.1 107.0 97.9 121.6 95.0 Fracture — — — — — — — Toughness(MPa · m^(1/2)) Young's Mod. 77.01 75.70 74.67 73.15 71.64 71.08 71.22(GPa) Composition Mole % Composition ID 92 93 94 95 96 97 98 SiO₂ 66.88267.005 66.936 66.907 67.010 66.976 66.996 Al₂O₃ 14.012 14.157 14.15014.117 13.974 14.129 14.122 B₂O₃ 5.660 5.417 5.608 5.121 4.581 3.8973.514 P₂O₅ 2.857 2.050 1.752 2.000 2.600 3.219 3.451 Li₂O 8.290 8.2008.071 8.271 8.222 8.178 8.354 Na₂O 2.191 3.073 3.380 3.489 3.509 3.4903.462 K₂O 0.003 0.003 0.003 0.003 0.003 0.003 0.003 MgO 0.020 0.0200.016 0.015 0.016 0.020 0.018 CaO 0.014 0.014 0.014 0.014 0.014 0.0140.014 ZnO 0.000 0.000 0.000 0.000 0.000 0.000 0.000 SnO₂ 0.052 0.0480.053 0.049 0.052 0.051 0.050 ZrO₂ 0.014 0.009 0.013 0.012 0.013 0.0170.011 TiO₂ 0.000 0.000 0.000 0.000 0.000 0.000 0.000 HfO₂ — — — — — — —Fe₂O₃ 0.004 0.004 0.004 0.004 0.004 0.004 0.004 MnO₂ 0.000 0.000 0.0000.000 0.000 0.000 0.000 SrO — — — — — — — R₂O—Al₂O₃ −3.527 −2.882 −2.697−2.354 −2.239 −2.458 −2.304 R₂O+RO—Al₂O₃ −3.493 −2.848 −2.666 −2.325−2.208 −2.423 −2.271 R₂O+RO+P₂O₅— −0.636 −0.797 −0.915 −0.326 0.3920.796 1.180 Al₂O₃ Li₂O/R₂O 0.791 0.727 0.705 0.703 0.701 0.701 0.707Strain (° C.) 553 555 554 556 554 559 557 Anneal (° C.) 608 609 608 610608 614 612 Softening (° C.) — 885.4 — — — — — CTE (10⁻⁷ ° C.⁻¹) — 50.8— — — — — Density (g/cm³) — 2.319 2.323 2.324 — — — Liq. T (° C.) 11451140 1130 1135 1135 1135 1115 Liq. Visc. (kP) 98.2 93.0 104.6 100.3116.3 138.4 197.7 Fracture — — — — — — — Toughness (MPa · m^(1/2))Young's Mod. 71.43 82.87 73.15 73.02 72.33 72.60 72.88 (GPa) CompositionMole % Composition ID 99 100 101 102 103 SiO₂ 67.305 67.833 68.61369.083 69.867 Al₂O₃ 14.017 13.832 13.418 13.260 12.943 B₂O₃ 3.676 3.6743.842 3.985 4.098 P₂O₅ 3.102 2.609 1.944 1.222 0.449 Li₂O 8.051 7.7937.481 7.101 6.709 Na₂O 3.479 3.516 3.484 3.617 3.645 K₂O 0.003 0.0030.003 0.003 0.003 MgO 0.152 0.351 0.597 0.853 1.127 CaO 0.144 0.3220.555 0.812 1.088 ZnO 0.000 0.000 0.000 0.000 0.000 SnO₂ 0.049 0.0510.046 0.047 0.043 ZrO₂ 0.018 0.013 0.010 0.011 0.022 TiO₂ 0.000 0.0000.000 0.000 0.000 HfO₂ — — — — — Fe₂O₃ 0.004 0.004 0.005 0.005 0.005MnO₂ 0.000 0.000 0.000 0.000 0.000 SrO — — — — — R₂O—Al₂O₃ −2.484 −2.520−2.450 −2.538 −2.585 R₂O+RO—Al₂O₃ −2.188 −1.848 −1.297 −0.873 −0.370R₂O+RO+P₂O₅— 0.914 0.761 0.647 0.349 0.079 Al₂O₃ Li20/R20 0.698 0.6890.682 0.662 0.648 Strain (° C.) 562 562 568 572 577 Anneal (° C.) 617616 622 626 631 Softening (° C.) — — — — 903.3 CTE (10⁻⁷ ° C.⁻¹) — — — —49.9 Density (g/cm³) 2.327 — 2.336 — 2.35 Liq. T (° C.) 1135 1140 11351145 1150 Liq. Visc. (kP) 140.5 131.2 147.5 120.6 110.1 Fracture — — — —— Toughness (MPa · m^(1/2)) Young's Mod. 74.19 73.50 74.19 75.70 76.95(GPa)

Example 2

Two sets of samples for each of three of the exemplary glasscompositions (compositions 26, 65, and 77) were further processed andion exchange strengthened. The compositions before ion exchange for eachof the three exemplary glass compositions are provided below in Table 2.One set of the samples for each of the exemplary glass compositions ofExample 2 was fictivated by heat treating the samples for 4 minutes at atemperature at which the viscosity of the glass composition is 10¹¹poise and then quenching the samples in flowing air at ambienttemperature. These fictivated samples are designed with suffix “-F” inTable 2 below. This thermal treatment mimics the thermal history of afusion drawn glass which is quenched. A second set of samples for eachexemplary glass composition of Example 2 was simply annealed. Thesesamples are designated in Table 2 with the suffix “-A.”

The samples were then ion exchanged to produce a parabolic stressprofile in each of the samples. Each of the samples of the glasscompositions in Example 2 had a thickness of 0.8 mm. Samples 26-F2,65-A, 65-F, 77-A, and 77-F were ion exchanged in a molten salt bathcomprising 80 weight percent (wt. %) KNO₃ and 20 wt. % NaNO₃. Sample26-F1 was ion exchanged in a molten salt bath comprising 100 wt. %NaNO₃. The samples were ion exchanged at a temperature of 430° C. for animmersion time sufficient to attain the parabolic stress profile. Theimmersion times for each sample are provided in Table 2 below.

TABLE 2 Compositions and Properties of the Glass Compositions of Example2 Sample No. 26-F1 26-F2 65-A 65-F 77-A 77-F Ref No. in FIG. 120 122 130132 140 142 2 SiO₂ 67.097 67.097 67.72 67.72 67.088 67.088 Al₂O₃ 13.97113.971 13.91 13.91 14.051 14.051 Li₂O 7.919 7.919 7.84 7.84 7.905 7.905Na₂O 1.931 1.931 1.92 1.92 1.978 1.978 K₂O 0.040 0.040 .03 .03 — — B₂O₃4.890 4.890 5.44 5.44 5.007 5.007 P₂O₅ 3.966 3.966 2.94 2.94 3.876 3.876MgO 0.025 0.025 .02 .02 0.028 0.028 CaO 0.046 0.046 .04 .04 0.014 0.014R₂O—Al₂O₃ −4.81 −4.81 −4.12 −4.12 −4.17 −4.17 (R₂O+RO— −4.00 −4.00 −4.06−4.06 −4.12 −4.12 Al₂O₃) R₂O+RO+ P₂O₅— −0.04 −0.04 −1.12 −1.12 −0.25−0.25 Al₂O₃ Li₂O/R₂O 0.80 0.80 .80 .80 0.80 0.80 Properties of the GlassCompositions Treatment fictivated fictivated annealed fictivatedannealed fictivated Strain T (° C.) 566 566 562 562 561 561 Anneal T (°C.) 623 623 618 618 618 618 Softening T (° C.) — — — — — — CTE (10⁻⁷/°C.) 47 47 — — — — Density (g/cc) 2.31 2.31 2.31 2.31 2.30 2.30 LiquidusT (° C.) 1100 1100 1160 1160 1100 1100 Liquidus 384.4 384.4 99.3 99.3371.4 371.4 Viscosity (kP) Young's 70.88 70.88 72.12 72.12 71.15 561Modulus (GPa) Na:K in Ion 100:0 20:80 20:80 20:80 20:80 20:80 ExchangeBath Bath Temp (° C.) 430 430 430 430 430 430 Ion Exchange Time (hr) 3 35 3.5 4 3 CS (MPa) — 401 434 403 425 413 DOL (μm) — 12.8 10.9 11.4 11.612.3 DOC (μm) 163 163 143 158 159 158 CT (MPa) 67 67 90 67 82 65

Referring to FIG. 1, the stress profiles for samples 77-A and 77-F as afunction of the position through the thickness of the glass samples areillustrated. The annealed glass of sample 77-A (reference no. 140 inFIG. 1) attained a higher central tension (CT) of 81.7 MPa, as shown inFIG. 1, but takes a longer ion exchange immersion time to achieve thepeak CT. The fictivated glass composition of sample 77-F (reference no.142 in FIG. 1) gets to peak CT in a shorter immersion time of only 3hours compared to 4 hours for sample 77-A. However, fictivated sample77-F exhibited a lower peak CT of 61.6 MPa. The results in FIG. 1 arefor samples ion exchanged in an ion exchange bath that included 80 wt. %KNOB and 20 wt. % NaNO₃. The same glass compositions achieve a peak CTof greater than 90 MPa when ion exchanged in 100% NaNO₃, but with lowercompressive stress at the surface.

It should now be understood that the glass compositions described hereinexhibit chemical durability as well as mechanical durability followingion exchange. These properties make the glass compositions well suitedfor use in various applications including, without limitation,pharmaceutical packaging materials.

It will be apparent to those skilled in the art that variousmodifications and variations can be made to the embodiments describedherein without departing from the spirit and scope of the claimedsubject matter. Thus it is intended that the specification cover themodifications and variations of the various embodiments described hereinprovided such modification and variations come within the scope of theappended claims and their equivalents.

1-50. (canceled)
 51. A glass article comprising a composition, thecomposition comprising: greater than or equal to 50 mol. % and less thanor equal to 80 mol. % SiO₂; greater than or equal to 7 mol. % and lessthan or equal to 25 mol. % Al₂O₃; greater than or equal to 2 mol. % andless than or equal to 14 mol. % Li₂O; greater than or equal to 3 mol. %and less than or equal to 15 mol. % B₂O₃; greater than or equal to 0.1mol. % Na₂O; and greater than 0 mol. % and less than or equal to 4 mol.% TiO₂, wherein (Al₂O₃ (mol. %)-R₂O (mol. %)-RO(mol. %)) is greater thanor equal to 0 mol. %, where R₂O (mol. %) is the sum of the molar amountsof Li₂O, Na₂O, K₂O, Rb₂O, and Cs₂O in the composition and RO (mol. %) isthe sum of the molar amounts of BeO, MgO, CaO, SrO, BaO, and ZnO in thecomposition, wherein (Al₂O₃ (mol. %)-R₂O (mol. %)-RO(mol. %)-P₂O₅ (mol.%)) is less than or equal to 2, and wherein R₂O (mol. %) is less than orequal to 14 mol. %.
 52. The glass article of claim 1, wherein a molarratio of (Li₂O (mol. %))/(R₂O (mol. %)) is greater than or equal to 0.5.53. The glass article of claim 1, wherein the composition furthercomprises greater than or equal to 0.4 mol. % and less than or equal to10 mol. % P₂O₅.
 54. The glass article of claim 3, wherein (Al₂O₃ (mol.%)-R₂O (mol. %)-RO(mol. %)-P₂O₅ (mol. %)) is greater than or equal to−2.
 55. The glass article of claim 1, wherein (Li₂O (mol. %)+Al₂O₃ (mol.%)) is greater than or equal to two times B₂O₃ (mol. %).
 56. The glassarticle of claim 1, wherein the composition further comprises greaterthan or equal to 1.5 mol. % and less than or equal to 6 mol. % Na₂O. 57.The glass article of claim 1, wherein the composition further comprisesless than or equal to 0.35 mol. % SnO₂.
 58. The glass article of claim1, wherein the composition has a liquidus temperature of less than orequal to 1300° C.
 59. The glass article of claim 1, wherein thecomposition has a liquidus viscosity of greater than 20 kP.
 60. Aconsumer electronic product, comprising: a housing having a frontsurface, a back surface and side surfaces; electrical componentsprovided at least partially within the housing, the electricalcomponents including at least a controller, a memory, and a display, thedisplay being provided at or adjacent the front surface of the housing;and a cover substrate disposed over the display, wherein at least one ofa portion of the housing or the cover substrate comprises the glassarticle of claim 1.